Semiconductive ceramic compositions with a nonlinear volt-ampere characteristic, and process for preparing coherent bodies of such compositions

ABSTRACT

Ceramic materials suitable for use in varistors, enabling the same to function both as such and as capacitors. The ceramic compositions comprise a major proportion of SrTiO 3 , the balance being (1) one or more of Nb 2  O 5 , Ta 2  O 5 , WO 3 , La 2  O 3 , CeO 2 , Nd 2  O 3 , Pr 6  O 11 , Dy 2  O 3 , Y 2  O 3 , and Sm 2  O 3 , for making the compositions semiconductive, and (2) one or more of V 2  O 5 , Cr 2  O 3 , CuO, Cu 2  O, MoO 3 , and MnO 2 , for improving the nonlinear volt-ampere characteristic of the compositions. If desired, for improving the coherency of bodies molded from the composition, there can be added one or more of GeO 2 , ZnO, B 2  O 3 , and PbO. For use as varistors the mixture of the above ingredients, all in finely divided form and made coherent with a binder, is molded into desired shape under pressure. The moldings are first fired in a nonoxidative atmosphere and then further heated in an oxidative atmosphere. Electrodes can be formed as by silver painting.

This is a division of application Ser. No. 280,801, filed July 6, 1981.

BACKGROUND OF THE INVENTION

This invention relates to ceramic materials particularly well suited foruse in semiconductor devices having a nonlinear volt-amperecharacteristic. The invention also concerns a process for thefabrication of coherent bonded bodies of such materials.

Semiconductor devices with a nonlinear volt-ampere characteristic findextensive use in electric circuits for the absorption of abnormalvoltages, suppression of noise, and elimination of sparks. Commonlyreferred to as varistors, as hereinafter so called in thisspecification, such semiconductor devices have been fabricated typicallyfrom silicon (using the pn-junctions of silicon semiconductors), siliconcarbide (SiC), zinc oxide (ZnO), stannic oxide (SnO₂), and titaniumdioxide (TiO₂).

The pn-junction silicon varistors make use of forward voltage rises, sothat they offer a varistor voltage of as low as 0.6 volt (V) or so perpn-junction. For higher varistor voltages, therefore, a plurality ofpn-junction silicon chips must be interconnected in series. As regardsthe SiC varistors, the nonlinearity coefficient α of their volt-amperecharacteristic is as low as two or three in a voltage range of 3-20 V.Another disadvantage is that SiC cannot possibly be sintered intoannular or other more or less complex shape with sufficient coherency.The ZnO varistors have a high nonlinearity coefficient in a voltagerange of over 30 V, but it becomes as low as about two in a low voltagerange of 3-20 V. The nonlinearity coefficient of the SnO₂ varistors ishigher, being up to about five, in the voltage range of 3-20 V. Thisadvantage is offset, however, by the poor sinterability, expensiveness,and low moisture-withstanding ability of the material. Moreover, sincethe SnO₂ varistors function as such by making use of the PN-junctions atthe interfaces between the electrodes and the semiconductor bodies,their physical properties tend to deteriorate from voltage pulses. TheTiO₂ varistors can be molded and sintered into any desired shape, buttheir nonlinearity coefficient is only two to four in a voltage range of20-30 V. Additionally, their varistor voltage varies with temperature(temperature characteristic) at a rate ranging from -0.5 to 0.7% per°C., and they are easy to overheat while handling large power.

Another known varistor material being studied is barium titanate(BaTiO₃). The BaTiO₃ varistors utilize the PN-junctions at theinterfaces between the electrodes and the semiconductor bodies, justlike the SnO₂ varistors, so that they possess drawbacks similar to thosepointed out in connection with the SnO₂ varistors.

For the purposes of the absorption of abnormal voltages and theelimination of noise and sparks, the parallel connections of varistorsand capacitors have hitherto served better than varistors only, as iswell known to the specialists. No ceramic composition having bothfunctions has so far been discovered, as far as the applicant is aware.Such a material will significantly contribute to the miniaturization andcost reduction of electrical equipment.

U.S. Pat. No. 3,933,668 issued to Takahashi et al. on Jan. 20, 1976,describes and claims a ferroelectric ceramic compound in a perovskitestructure, composed principally of strontium titanate (SrTiO₃). Thisknown ceramic material is well suited for use in capacitors. The highresistance offered by the particles constituting the ceramic, however,practically inhibits its use in varistors. Another disadvantage of theknown SrTiO₃ ceramic is easy deterioration of electrical properties dueto voltage pulses.

SUMMARY OF THE INVENTION

The present invention seeks to combine both varistor and capacitorfunctions in a single class of semiconductive ceramic compositions, andto provide such compositions themselves and a process for thefabrication of coherent bonded bodies of such compositions.

The invention also seeks to provide semiconductive ceramic materialswhich are capable of providing such a low range of varistor voltages as,say, from three to 100 V, which are little affected physically byvoltage pulses in their use in semiconductor devices, and which,manufactured by the inventive method, hardly fluctuate in electricalproperties.

Briefly, the invention provides a semiconductive ceramic compositioncomprising: (1) from about 90.000 to about 99.989 mole percent SrTiO₃(hereinafter referred to as the first or main ingredient); (2) fromabout 0.001 to about 5.000 mole percent of at least one metal oxide (thesecond ingredient), for improving the semiconductivity of thecomposition, which is selected from the group of niobium oxide (Nb₂ O₅),tantalum oxide (Ta₂ O₅), tungstic oxide (WO₃), lanthanum oxide (La₂ O₃),ceric oxide (CeO₂), neodymium oxide (Nd₂ O₃), praseodymia (Pr₆ O₁₁),dysprosium oxide (Dy₂ O₃), yttrium oxide (Y₂ O₃), and samarium oxide(Sm₂ O₃); and (3) from about 0.010 to about 5.000 mole percent of atleast one other metal oxide (the third ingredient), for improving thenonlinear volt-ampere characteristic of the composition, which isselected from the group of vanadium pentoxide (V₂ O₅), chromic oxide(Cr₂ O₃), black copper oxide (CuO), red copper oxide (Cu₂ O), molybdenumtrioxide (MoO₃), and manganese dioxide (MnO₂).

Hereinafter in this specification and in the claims appended thereto,all percentages are molar unless otherwise specified.

The exact proportion of each of the at least three ingredients of theceramic composition according to the invention depends on those of theothers. Preferably, the main ingredient is used in a range of about97.7-99.1%, the second ingredient in a range of about 0.3-1.0%, and thethird ingredient in a range of about 0.1-0.3%, in proportions.

In the above described ceramic composition according to the invention,the addition of at least one of the third group of ingredients (V₂ O₅,Cr₂ O₃, CuO, Cu₂ O, MoO₃, and MnO₂) to the first and second ingredientsserves to give the material a markedly nonlinear volt-amperecharacteristic, or voltage-dependent nonlinear resistance. The crystalsystem of the material is in a ferroelectric perovskite structure, sothat it offers a high electrostatic capacitance, making it possible toprovide semiconductor devices integrally combining the functions of bothvaristor and capacitor.

It is reasoned that the ceramic materials formulated in accordance withthe invention derive their varistor-like characteristics from thePN-junctions between their constituent particles, with the N-typesemiconductor particles of, principally, the first and secondingredients surrounded by the third ingredient of P type or ofsubstantially P type. Consequently, compared with the known varistorshaving the PN-junctions formed between the ceramic bodies and theelectrodes, the varistors incorporating the ceramic materials of thisinvention will suffer less from voltage pulses. A further advantage ofthe ceramic compositions according to the invention is theinexpensiveness of their main ingredient, SrTiO₃, making possible theprovision of high-quality varistor ceramics at low costs.

According to another aspect of the invention the above compositions ofat least three ingredients are admixed with at least one still othermetal oxide (hereinafter referred to as the fourth ingredient) with aview to higher coherency of the ceramic bodies prepared from thecompositions. The fourth ingredient is selected from the group ofgermanium dioxide (GeO₂), zinc oxide (ZnO), boric oxide (B₂ O₃), andlitharge (PbO). The fourth ingredient serves to make the particles ofthe sintered ceramic bodies from about 20 to 40 microns in size, andfurther to improve the voltage rises of their V-I curves and to reducefluctuations in the nonlinearity coefficient. The proportion of thefourth ingredient, dependent on those of the other ingredients, normallyranges from about 0.010 to about 4.000%, preferably from about 0.5 toabout 1.0%. When a ceramic composition contains from about 0.010 toabout 4.000% of the fourth ingredient, the amount of the firstingredient is correspondingly reduced to a range of about86.000-99.979%.

For the fabrication of coherent bonded bodies of the first describedcomposition (having no fourth ingredient) by the method of thisinvention, SrTiO₃ and at least two selected metal oxides of theprescribed proportions, all in finely divided form, are blended togetherand admixed with an organic binder. The blended mixture is molded intodesired shape, such as that of a disc, at pressures ranging from about500 to about 2000 kg/cm². The molding is first fired in a temperaturerange of about 1300°-1500° C. in a nonoxidative (i.e., reductive orneutral) atmosphere and then further heated in a temperature range ofabout 800°-1300° C. in an oxidative atmosphere.

If the composition includes a fourth ingredient or ingredients, thetemperature of the oxidative heat treatment of the fired molding isselected from a range of about 900°-1300° C. In other respects, coherentbodies of this four-ingredient composition can be formed by the samemethod as are those of the three-ingredient composition.

The ceramic bodies manufactured by the methods of this invention areremarkably well suited for varistors, besides being notable for theirhigh abilities of absorbing abnormal voltages in use. Subsequentlyelectroded, the ceramic bodies find use as varistors.

The above and other features and advantages of this invention willbecome more apparent, and the invention itself will best be understood,from the following description and appended claims taken together withthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a varistor incorporating aceramic body formulated in accordance with the invention;

FIG. 2 is a graphic representation of the volt-ampere characteristic ofan SrTiO₃ --CeO₂ --V₂ O₅ varistor fabricated in EXAMPLE 1 of theinvention;

FIG. 3 is a graph representing the degrees of attenuation of variousmegahertz frequencies by the SrTiO₃ --CeO₂ --V₂ O₅ varistor, incomparison with the attenuation characteristic of a known ZnO varistor,as tested in EXAMPLE 1 of the invention;

FIG. 4 is a graph plotting the curve of the varistor voltage E₁₀ ofSrTiO₃ --Nb₂ O₅ --CuO varistors against the varying percentages of theirCuO content, with their Nb₂ O₅ content fixed at 0.1%, as tested inEXAMPLE 3 of the invention;

FIG. 5 is a graph plotting the curve of the varistor voltage E₁₀ ofSrTiO₃ --Nb₂ O₅ --CuO varistors against the varying percentages of theirNb₂ O₅ content, with their CuO content fixed at 0.01%, also as tested inEXAMPLE 3 of the invention;

FIG. 6 is a graph plotting the curve of the volt-ampere nonlinearitycoefficient α of SrTiO₃ --Nb₂ O₅ --CuO varistors against thetemperatures at which they were subjected to oxidative heat treatment inmanufacture, as tested in EXAMPLE 13 of the invention;

FIG. 7 is a graph plotting the curve of the α of SrTiO₃ --Nb₂ O₅--CuO--GeO₂ varistors against the temperatures at which they weresubjected to oxidative heat treatment in manufacture, as tested inEXAMPLE 23 of the invention;

FIG. 8 is a graph plotting the curve of the E₁₀ of the SrTiO₃ --Nb₂ O₅--CuO--GeO₂ varistors against the temperatures at which they weresubjected to oxidative heat treatment in manufacture, in comparison withthe curve representing similar relationship in the case of the SrTiO₃--Nb₂ O₅ --CuO varistors, also as tested in EXAMPLE 23 of the invention;and

FIG. 9 is a graph plotting the curves of the rates of change in the E₁₀of SrTiO₃ --Nb₂ O₅ --CuO--GeO₂ and SrTiO₃ --Nb₂ O₅ --MoO₃ --GeO₂varistors with the temperatures at which they were put to use, as testedin EXAMPLE 25 of the invention.

DETAILED DESCRIPTION

The compositions of the semiconductive ceramic materials according tothis invention are as set forth in the foregoing summary of theinvention. The fabrication of coherent bonded bodies of suchcompositions, as in the form of discs for use in varistors, starts withthe preparation of SrTiO₃, the main ingredient, which occupies a majorproportion in all the possible combinations of ingredients in accordancewith the invention. This main ingredient is usually prepared fromstrontium carbonate (SrCO₃) and titanium dioxide (TiO₂), proportioned tounite into SrTiO₃. SrCO₃ and TiO₂ do so by being fired at temperaturesranging from 1050° to 1200° C. for three hours.

If the composition is to include no fourth ingredient, from about 90.000to about 99.989% SrTiO₃, prepared as above, is combined with about0.001-5.000% of at least one metal oxide (second ingredient) selectedfrom the group of Nb₂ O₅, Ta₂ O₅, WO₃, La₂ O₃, CeO₂, Nd₂ O₃, Pr₆ O₁₁,Dy₂ O₃, Y₂ O₃, and Sm₂ O₃, and with about 0.010-5.000% of at least oneother metal oxide (third ingredient) selected from the group of V₂ O₅,CrO₃, CuO, Cu₂ O, MoO₃, and MnO₂. The combination of at least threeingredient is pulverized and intimately intermingled by being placed ina ball mill for 10 hours or so. The blended mixture of finely dividedform is then admixed with 5-10 percent by weight of an organic binder,normally polyvinyl alcohol. This admixture is molded into disc-like orother desired shape by pressing at about 500-2000 kg/cm².

Then the moldings are fired in a temperature range of about 1300°-1500°C., preferably about 1350°-1420° C., for 1-6 hours in a nonoxidativeatmosphere. The total firing time, inclusive of the time for the buildupand drop of the firing temperature in the furnace, may be from 24 to 48hours. The firing atmosphere is reductive for the better results,consisting for example of 95 percent by volume of molecular nitrogen(N₂) and five percent by volume of molecular hydrogen (H₂). The firedmoldings are put to oxidative heat treatment (reoxidizing treatment), bybeing heated in a temperature range of about 800°-1300° C., preferablyabout 800°-1170° C., for 0.5-6.0 hours in an oxidative atmosphere. Thetotal time of such oxidative heat treatment, inclusive of the time forthe buildup and drop of the heating temperature in the furnace, mayrange from four to eight hours. Thus are completed the desired ceramicbodies, which can be put to use as varistors on being electroded, as bysilver painting and baking.

In the EXAMPLES of the invention presented subsequently, all but CrO₃ ofthe listed metal oxides are used as such as starting materials. All thatis required for the attainment of the purposes of this invention,however, is that the completed ceramic bodies contain the selected metaloxides. The starting materials may therefore be not necessarily in theform of metal oxides but of, for example, metallic elements, carbonates,hydroxides, oxalates, etc. To give more specific examples, the firstingredient may be formed from starting substances of strontium andtitanium; the second ingredient from such starting substances as Nb(HC₂O₄)₅, La₂ (C₂ O₄)₃, La₂ (CO₃)₃, Ce₂ (C₃ O₄)₃, Ce₂ (CO₃)₃, Pr₂ (C₂ O₄)₃,Nd₂ (C₂ O₄)₃, Nd₂ (CO₃)₃, Sm₂ (C₂ O₄)₃, Sm₂ (CO₃)₃, Dy₂ (C₂ O₄)₃, Dy₂(CO₃)₃, and Y₂ (CO₃)₃ ; and the third ingredient from such startingsubstances as CuCO₃, CuC₂ O₄, CuCN, Cu₂ S, Cr₂ (CH₃ COO)₃, Cr₂ (SO₃)₃,V₂ S₃, Mo(OH)₃, Mo(OH)₅, MnCO₃, and MoC₂ O₄.

The invention also dictates the use, in combination with the first,second and third ingredients, of at least one additional metal oxideselected from the group of GeO₂, ZnO, B₂ O₃, and PbO. The metal oxidechosen as the fourth ingredient is also required to exist as such in thecompleted ceramics, so that it may be formed from such startingsubstances as Ge(OH)₂, ZnC₂ O₄, 5ZnO₂ CO₃ 4H₂ O, PbC₂ O₄, and (PbCO₃)₂Pb(OH)₂.

The following EXAMPLES will provide further details of the compositionsand manufacturing methods of the ceramic materials in accordance withthe invention, as well as the characteristics of varistors incorporatingthe ceramic materials.

EXAMPLE 1

SrCO₃ and TiO₂, proportioned to combine into SrTiO₃, were fired in atemperature range of 1050°-1200° C. for three hours. The firedsubstances were pulverized by means of a crusher, thus providing SrTiO₃as the first ingredient of the desired ceramic materials. This firstingredient was combined with CeO₂ as the second ingredient and V₂ O₅ asthe third ingredient, in various proportions set forth in TABLE 1,wherein the Test Numbers refer to the combinations of the threeingredients in various proportions.

Each combination of the three ingredients, which were all in finelydivided form, was then admixed with 5-10 wt. % polyvinyl alcohol, anorganic binder. The admixtures were molded at pressures ranging from 500to 2000 kg/cm² into the form of discs each sized to have a diameter of 5millimeters (mm) and a thickness of 0.8 mm on firing.

Then the moldings were fired for three hours at a temperature of 1390°C., by being placed within a furnace for a total of 32 hours, in areductive atmosphere of 95 vol. % N₂ and five vol. % H₂. The firingtemperatures could be anywhere between about 1300° and about 1500° C.,and the firing time could be from one to six hours depending upon thefiring temperature selected. Then, in order to control the varistorvoltage (rising voltage of the voltage-current curve) of the endproducts, the fired moldings were treated at a temperature of 900° C.for two hours in an oxidative atmosphere of air, by being placed withina furnace for a total of six hours. This oxidizing heat treatment couldbe effected in a temperature range of about 800°-1300° C., for a lengthof time ranging from about 0.5 to 6.0 hours depending upon thetemperature.

Then, as illustrated in FIG. 1, each disc-like ceramic body 1 composedand fabricated in accordance with the invention had its opposite facescoated with silver paint to be processed into a varistor. The silvercoatings were baked in a temperature range of 400°-1000° C. into a pairof electrodes 2 and 3, thus completing the desired varistor. Thevaristor according to this invention derives its intended functions fromthe interior of the sintered body itself, so that the electrodes 2 and 3could be made from other materials such as indium-gallium alloy, and byother methods such as evaporation or plating.

The ceramic body 1 of the varistor prepared as above comprises fine,conductive crystal grains 4 dispersed in a resistive oxide region 5,just like the ZnO varistor ceramic. The nonlinearity of its volt-amperecharacteristic results as the first ingredient, SrTiO₃, is acted upon bythe second, CeO₂, and third, V₂ O₅, ingredients. Although the exactreason for this is not necessarily clear, a fairly reasonable theorywould be that the second ingredient acts on the minute crystal particles4 of the first ingredient to provide N-type semiconductors, whereas theoxide region 5, composed principally of the third ingredient, provides aP-type semiconductor.

Polyvinyl alcohol was used to bind the three pulverized ingredients inmolding them into disc-like shape. This organic binder evaporates or isburnt out by the subsequent heat treatments of the moldings.Consequently the composition of the completed ceramic body 1 essentiallycorresponds to the starting substances only.

The characteristics of the varistors of this class might be evaluatedfrom α and K in the volt-ampere characteristic formula of varistors ingeneral, I=(V/K).sup.α, where I is the varistor current, V the appliedvoltage, K a constant, and α a coefficient indicative of thevoltage-current nonlinearity. Exact measurement of K is difficult,however, so that the characteristics of the above prepared varistorswere ascertained from the varistor voltage E₁₀ when a current of 10 mAwas flowing, and from α=1/log (E₁₀ /E₁), where E₁ is the varistorvoltage corresponding to the current of 1 mA. The following TABLE 1represents the various sets of proportions of the three notedingredients used to produce the varistors in this EXAMPLE 1, togetherwith their varistor voltage E₁₀, nonlinearity coefficient α, andelectrostatic capacity C. The electrostatic capacities of the varistorswere measured at a frequency of 1 kHz.

                  TABLE 1                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            CeO.sub.2                                                                              V.sub.2 O.sub.5                                                                      E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   13     6    49                                 2     99.94    0.05     0.01   5      5    51                                 3     99.89    0.10     0.01   4      4    63                                 4     98.99    1.00     0.01   7      5    57                                 5     94.99    5.00     0.01   12     6    50                                 6     99.94    0.01     0.05   20     7    52                                 7     99.90    0.05     0.05   7      6    66                                 8     99.85    0.10     0.05   6      5    76                                 9     98.95    1.00     0.05   11     6    62                                 10    94.95    5.00     0.05   18     7    53                                 11    99.89    0.01     0.10   32     11   46                                 12    99.85    0.05     0.10   12     6    57                                 13    99.80    0.10     0.10   10     6    61                                 14    98.90    1.00     0.10   17     7    56                                 15    94.90    5.00     0.10   29     9    47                                 16    99.49    0.01     0.50   64     20   37                                 17    99.45    0.05     0.50   25     8    50                                 18    99.40    0.10     0.50   20     7    51                                 19    98.50    1.00     0.50   36     11   46                                 20    94.50    5.00     0.50   61     20   33                                 21    98.99    0.01     1.00   106    35   26                                 22    98.95    0.05     1.00   45     13   41                                 23    98.90    0.10     1.00   36     12   39                                 24    98.00    1.00     1.00   63     21   31                                 25    94.00    5.00     1.00   101    34   21                                 ______________________________________                                    

FIG. 2 graphically represents by way of example the volt-amperecharacteristic of the varistor of Test No. 13 given in TABLE 1.

The varistor of Test No. 13 was also evaluated as to the attenuation ofvarious megahertz frequencies, by connecting the varistor in parallelwith a signal generator and with a spectrum analyzer. The curve A in thegraph of FIG. 3 represents the results. The curve B in the same graphindicates, by way of comparison, the damping characteristic (measured bythe same method as above) of a varistor having its ceramic body composedprincipally of ZnO. A comparison of the curves A and B will reveal thatthe varistor according to this invention has a higher damping abilityover a wide frequency range, thus exhibiting a capacitor-like property.The inventive material is therefore capable of absorbing voltage surges,noise, etc., by acting as both varistor and capacitor.

Although only the varistor of Test No. 13 was experimented as to itscapacitor-like property, it is obvious that all the other varistorsfabricated in this EXAMPLE 1 have a similar property, for their varistorvoltages E₁₀ all fall between four and 106 V, their voltage-currentnonlinearity coefficients α between four and 35, and their electrostaticcapacity C between 21 and 76 nF.

In thus producing the SrTiO₃ --CeO₂ --V₂ O₅ varistors proportioned as inTABLE 1, it has proved that if the proportion of the third ingredient,V₂ O₅, is less than about 0.01%, the material introduces considerablefluctuations in the varistor voltage E₁₀ and nonlinearity coefficient αof the resulting products, making it difficult to provide varistors ofdesired properties. If the proportion of V₂ O₅ exceeds about 1%, on theother hand, the resistive oxide region 5 of FIG. 5 has proved to occupyan unduly large space, with the V₂ O₅ present at the surfaces causingfusion of the adjacent ceramic bodies to each other.

EXAMPLE 2

Ceramic bodies were fabricated from a combination of SrTiO₃ as the firstingredient, WO₃ as the second ingredient, and CrO₃ as the thirdingredient, and were processed into varistors, through exactly the sameprocedure as in EXAMPLE 1. TABLE 2 indicates the various sets ofproportions of the three ingredients used to produce the ceramic bodies,together with the varistor voltage E₁₀, voltage-current nonlinearitycoefficient α, and electrostatic capacity C of the correspondingvaristors. These properties of the varistors were also measured by thesame method as in EXAMPLE 1.

                  TABLE 2                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            WO.sub.3 CrO.sub.3                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   7      4    64                                 2     99.94    0.05     0.01   4      4    71                                 3     99.89    0.10     0.01   2      4    84                                 4     98.99    1.00     0.01   5      4    80                                 5     97.49    2.50     0.01   9      5    76                                 6     99.94    0.01     0.05   11     6    72                                 7     99.90    0.05     0.05   7      5    85                                 8     99.85    0.10     0.05   3      4    101                                9     98.95    1.00     0.05   9      5    92                                 10    97.45    2.50     0.05   15     7    90                                 11    99.89    0.01     0.10   17     7    66                                 12    99.85    0.05     0.10   9      5    80                                 13    99.80    0.10     0.10   5      4    108                                14    98.90    1.00     0.10   13     6    99                                 15    97.40    2.50     0.10   22     8    81                                 16    98.99    0.01     1.00   43     13   53                                 17    98.95    0.05     1.00   25     8    66                                 18    98.90    0.10     1.00   13     6    73                                 19    98.00    1.00     1.00   33     10   62                                 20    96.50    2.50     1.00   55     16   70                                 21    97.99    0.01     2.00   55     15   46                                 22    97.95    0.05     2.00   32     10   59                                 23    97.90    0.10     2.00   15     7    64                                 24    97.00    1.00     2.00   41     12   59                                 25    95.50    2.50     2.00   74     22   57                                 ______________________________________                                    

In the preparation of the ceramic bodies according to EXAMPLE 2 theoxidative heat treatment of the fired moldings converted the CrO₃ intoCr₂ O₃. When the proportion of CrO₃ was made less than about 0.01% theE₁₀ and α of the resulting varistors fluctuated considerably. Also, whenits proportion was made greater than about 2%, the relative spaceoccupied by the resistive oxide region 5 became too large, and the Cr₂O₃ at the surfaces of the moldings caused their adhesion to each other.

EXAMPLE 3

SrTiO₃ was employed as the first ingredient, Nb₂ O₅ as the secondingredient, and Cuo as the third ingredient. Combined in various sets ofproportions listed in TABLE 3, these ingredients were treated intoceramic bodies, and further into varistors, through exactly the sameprocedure as in EXAMPLE 1. TABLE 3 also shows the E₁₀, and C of thevaristors, as ascertained by the same method as in EXAMPLE 1.

                  TABLE 3                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       CuO    E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   10     5    80                                 2     99.94    0.05     0.01   5      5    81                                 3     99.89    0.10     0.01   3      4    96                                 4     98.99    1.00     0.01   6      5    62                                 5     97.49    2.50     0.01   13     6    76                                 6     99.94    0.01     0.05   11     6    99                                 7     99.90    0.05     0.05   6      5    109                                8     99.85    0.10     0.05   3      4    116                                9     98.95    1.00     0.05   7      5    102                                10    97.45    2.50     0.05   14     6    89                                 11    99.89    0.01     0.10   12     6    79                                 12    99.85    0.05     0.10   6      5    93                                 13    99.80    0.10     0.10   4      4    107                                14    98.90    1.00     0.10   8      5    93                                 15    97.40    2.50     0.10   16     7    80                                 16    98.99    0.01     1.00   36     18   66                                 17    98.95    0.05     1.00   18     8    72                                 18    98.90    0.10     1.00   11     6    90                                 19    98.00    1.00     1.00   22     9    81                                 20    96.50    2.50     1.00   47     21   77                                 21    94.99    0.01     5.00   73     30   52                                 22    94.95    0.05     5.00   36     17   61                                 23    94.90    0.10     5.00   23     9    73                                 24    94.00    1.00     5.00   45     20   62                                 25    92.50    2.50     5.00   95     37   61                                 ______________________________________                                    

An inspection of TABLE 3 will show that the percentage of Nb₂ O₅ isfixed at 0.1 in some tests, while in others the percentage of CuO isfixed at 0.01. FIG. 4 graphically represents the curve of the E₁₀ ofthose varistors whose Nb₂ O₅ content is fixed at 0.1%, plotted againstthe varying percentages of their CuO content. FIG. 5, on the other hand,plots the curve of the E₁₀ of those varistors whose CuO content is fixedat 0.01%, against the varying percentages of their Nb₂ O content.

A decrease of the CuO content to less than about 0.01% causedsubstantial fluctuations in the E₁₀ and α of the resulting varistors.The CuO content of over 5%, on the other hand, made too large therelative space occupied by the resistive oxide region 5 of eachvaristor, and caused mutual adhesion of the adjacent ceramic moldingsthrough the CuO lying at their surfaces.

EXAMPLE 4

Disc-like ceramic bodies were fabricated from SrTiO₃ as the firstingredient, Dy₂ O₃ as the second ingredient, and Cu₂ O as the thirdingredient, in various sets of proportions, and were processed intovaristors, through exactly the same procedure as in EXAMPLE 1. TABLE 4represents the proportions of the three ingredients, as well as the E₁₀,α, and C of the resulting varistors, as measured by the same method asin EXAMPLE 1.

                  TABLE 4                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Dy.sub.2 O.sub.3                                                                       Cu.sub.2 O                                                                           E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   7      4    57                                 2     99.94    0.05     0.01   4      4    63                                 3     99.89    0.10     0.01   2      4    73                                 4     98.99    1.00     0.01   5      4    70                                 5     97.49    2.50     0.01   9      5    51                                 6     99.94    0.01     0.05   11     6    68                                 7     99.90    0.05     0.05   7      5    74                                 8     99.85    0.10     0.05   3      4    89                                 9     98.95    1.00     0.05   9      5    69                                 10    97.45    2.50     0.05   15     7    58                                 11    99.89    0.01     0.10   17     7    51                                 12    99.85    0.05     0.10   9      5    67                                 13    99.80    0.10     0.10   5      4    71                                 14    98.90    1.00     0.10   13     6    63                                 15    97.40    2.50     0.10   22     8    53                                 16    98.99    0.01     1.00   43     13   47                                 17    98.95    0.05     1.00   25     8    59                                 18    98.90    0.10     1.00   13     6    63                                 19    98.00    1.00     1.00   33     10   54                                 20    96.50    2.50     1.00   55     16   47                                 21    97.99    0.01     2.00   55     15   36                                 22    97.95    0.05     2.00   32     10   48                                 23    97.90    0.10     2.00   15     7    51                                 24    97.00    1.00     2.00   41     12   42                                 25    95.50    2.50     2.00   73     22   30                                 ______________________________________                                    

A decrease of the Cu₂ O content to less than about 0.01% in the abovecombination caused substantial fluctuations in the E₁₀ and α of theresulting varistors. When the Cu₂ O content was made greater than about2.5%, on the other hand, the resistive oxide region 5 occupied too largea space, causing the thermal fusion to each other of the adjacentceramic moldings through the Cu₂ O at their surfaces.

EXAMPLE 5

Ceramic discs were fabricated from SrTiO₃ as the first ingredient, La₂O₃ as the second ingredient, and MoO₃ as the third ingredient, invarious sets of proportions, and were processed into varistors, throughexactly the same procedure as in EXAMPLE 1. TABLE 5 lists theproportions of the three ingredients, together with the E₁₀, α, and C ofthe varistors made therefrom, as measured by the same method as inEXAMPLE 1. Experiment has proved that the MoO₃ content of the ceramicmaterials in the above combination should be from about 0.01 to about5.00%, for falling outside this range, MoO₃ gave rise to the samedifficulties as those pointed out in the foregoing EXAMPLES.

                  TABLE 5                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            La.sub.2 O.sub.3                                                                       MoO.sub.3                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   8      4    54                                 2     99.94    0.05     0.01   4      3    61                                 3     99.89    0.10     0.01   3      3    76                                 4     98.99    1.00     0.01   5      4    69                                 5     97.49    2.50     0.01   7      4    50                                 6     99.94    0.01     0.05   22     7    63                                 7     99.90    0.05     0.05   11     5    73                                 8     99.85    0.10     0.05   9      5    81                                 9     98.95    1.00     0.05   14     6    70                                 10    97.45    2.50     0.05   20     7    56                                 11    99.89    0.01     0.10   53     15   49                                 12    99.85    0.05     0.10   28     9    67                                 13    99.80    0.10     0.10   19     7    70                                 14    98.90    1.00     0.10   36     11   58                                 15    97.40    2.50     0.10   47     13   48                                 16    98.99    0.01     1.00   53     15   43                                 17    98.95    0.05     1.00   28     9    51                                 18    98.90    0.10     1.00   19     7    61                                 19    98.00    1.00     1.00   36     11   54                                 20    96.50    2.50     1.00   47     13   41                                 21    94.99    0.01     5.00   89     30   30                                 22    94.95    0.05     5.00   46     13   42                                 23    94.90    0.10     5.00   34     10   48                                 24    94.00    1.00     5.00   57     17   40                                 25    92.50    2.50     5.00   79     25   27                                 ______________________________________                                    

EXAMPLE 6

Ceramic discs were fabricated from SrTiO₃ as the first ingredient, Ta₂O₅ as the second ingredient, and MnO₂ as the third ingredient, invarious combinations of proportions, and were processed into varistors,through exactly the same procedure as in EXAMPLE 1. TABLE 6 gives theproportions of the above three ingredients, together with the E₁₀, and Cof the varistors made therefrom, as measured by the same method as inEXAMPLE 1. It has also been found that the MnO₂ content of the ceramicdiscs in the above combination, if outside the range of about0.01-2.50%, gives rise to the difficulties mentioned previously.

                  TABLE 6                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Ta.sub.2 O.sub.5                                                                       MnO.sub.2                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1      99.985  0.005    0.01   9      5    63                                 2     99.94    0.05     0.01   4      4    71                                 3     99.49    0.50     0.01   2      3    81                                 4     98.99    1.00     0.01   5      4    73                                 5     97.49    2.50     0.01   8      5    61                                 6      99.945  0.005    0.05   16     7    68                                 7     99.90    0.05     0.05   7      5    79                                 8     99.45    0.50     0.05   4      4    96                                 9     98.95    1.00     0.05   9      5    82                                 10    97.45    2.50     0.05   14     6    77                                 11     99.895  0.005    0.10   23     8    70                                 12    99.85    0.05     0.10   11     5    86                                 13    99.40    0.50     0.10   7      5    101                                14    98.90    1.00     0.10   14     6    60                                 15    97.40    2.50     0.10   21     7    58                                 16     98.995  0.005    1.00   59     17   54                                 17    98.95    0.05     1.00   27     10   76                                 18    98.50    0.50     1.00   13     6    90                                 19    98.00    1.00     1.00   34     10   61                                 20    96.50    2.50     1.00   51     15   49                                 21     97.495  0.005    2.50   91     32   49                                 22    97.45    0.05     2.50   42     13   61                                 23    97.00    0.50     2.50   21     8    73                                 24    96.50    1.00     2.50   53     16   54                                 25    95.00    2.50     2.50   83     27   44                                 ______________________________________                                    

EXAMPLE 7

Ceramic discs were fabricated from SrTiO₃ as the first ingredient, Sm₂O₃ as the second ingredient, and CuO as the third ingredient, in variouscombinations of proportions, and were processed into varistors, throughexactly the same procedure as in EXAMPLE 1. TABLE 7 lists theproportions of the above three ingredients, together with the E₁₀, α,and C of the varistors made therefrom, as measured by the same method asin EXAMPLE 1.

                  TABLE 7                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Sm.sub.2 O.sub.3                                                                       CuO    E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   8      5    54                                 2     99.94    0.05     0.01   4      4    63                                 3     99.89    0.10     0.01   3      4    72                                 4     98.99    1.00     0.01   6      4    69                                 5     96.99    3.00     0.01   10     5    60                                 6     99.94    0.01     0.05   12     6    46                                 7     99.90    0.05     0.05   6      5    72                                 8     99.85    0.10     0.05   4      4    81                                 9     98.95    1.00     0.05   9      5    86                                 10    96.95    3.00     0.05   14     6    63                                 11    99.89    0.01     0.10   18     7    41                                 12    99.85    0.05     0.10   9      5    65                                 13    99.80    0.10     0.10   7      5    73                                 14    98.90    1.00     0.10   13     6    70                                 15    96.90    3.00     0.10   22     8    59                                 16    98.99    0.01     1.00   43     12   37                                 17    98.95    0.05     1.00   19     7    53                                 18    98.90    0.10     1.00   16     7    61                                 19    98.00    1.00     1.00   29     8    72                                 20    96.00    3.00     1.00   48     13   42                                 21    94.99    0.01     5.00   71     23   40                                 22    94.95    0.05     5.00   35     11   49                                 23    94.90    0.10     5.00   28     9    60                                 24    94.00    1.00     5.00   51     15   54                                 25    92.00    3.00     5.00   93     31   39                                 ______________________________________                                    

EXAMPLE 8

Ceramic discs were fabricated from SrTiO₃ as the first ingredient, Pr₆O₁₁ as the second ingredient, and MnO₂ as the third ingredient, invarious combinations of proportions, and were processed into varistors,through exactly the same procedure as in EXAMPLE 1. TABLE 8 lists theproportions of the above three ingredients, together with the E₁₀, α,and C of the varistors made therefrom, as measured by the same method asin EXAMPLE 1.

                  TABLE 8                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Pr.sub.6 O.sub.11                                                                      MnO.sub.2                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1      99.989  0.001    0.01   10     5    68                                 2     99.98    0.01     0.01   5      4    71                                 3     99.89    0.10     0.01   2      4    84                                 4     98.99    1.00     0.01   6      5    76                                 5     97.49    2.50     0.01   11     6    70                                 6      99.949  0.001    0.05   15     6    74                                 7     99.94    0.01     0.05   7      5    77                                 8     99.85    0.10     0.05   3      4    91                                 9     98.95    1.00     0.05   9      5    83                                 10    97.45    2.50     0.05   17     7    77                                 11     99.899  0.001    0.10   22     8    60                                 12    99.89    0.01     0.10   11     6    68                                 13    99.80    0.10     0.10   5      5    82                                 14    98.90    1.00     0.10   13     6    71                                 15    97.40    2.50     0.10   24     8    69                                 16     98.999  0.001    1.00   48     12   51                                 17    98.99    0.01     1.00   24     8    53                                 18    98.90    0.10     1.00   9      5    76                                 19    98.00    1.00     1.00   29     9    63                                 20    96.50    2.50     1.00   52     15   61                                 21     97.499  0.001    2.50   88     24   29                                 22    97.49    0.01     2.50   43     11   44                                 23    97.40    0.10     2.50   17     7    54                                 24    96.50    1.00     2.50   43     13   50                                 25    95.00    2.50     2.50   97     31   42                                 ______________________________________                                    

EXAMPLE 9

Ceramic discs were fabricated from SrTiO₂ as the first ingredient, Nd₂O₃ as the second ingredient, and CrO₃ as the third ingredient, invarious combinations of proportions, and were processed into varistors,through exactly the same procedure as in EXAMPLE 1. TABLE 9 lists theproportions of the above three ingredients, together with the E₁₀, α,and C of the varistors made therefrom, as measured by the same method asin EXAMPLE 1. In the preparation of of the ceramic discs according tothis EXAMPLE 9 the oxidative heat treatment of the fired moldingsconverted the CrO₃ into Cr₂ O₃.

                  TABLE 9                                                         ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Nd.sub.2 O.sub.3                                                                       CrO.sub.3                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   7      5    66                                 2     99.94    0.05     0.01   3      4    69                                 3     99.89    0.10     0.01   2      4    77                                 4     98.99    1.00     0.01   5      5    71                                 5     95.99    4.00     0.01   11     6    63                                 6     99.94    0.01     0.05   10     6    69                                 7     99.90    0.05     0.05   4      4    78                                 8     99.85    0.10     0.05   4      4    88                                 9     98.95    1.00     0.05   7      5    76                                 10    95.95    4.00     0.05   17     7    69                                 11    99.89    0.01     0.10   15     7    65                                 12    99.85    0.05     0.10   7      5    71                                 13    99.80    0.10     0.10   5      4    76                                 14    98.90    1.00     0.10   12     6    70                                 15    95.90    4.00     0.10   23     8    61                                 16    98.99    0.01     1.00   34     10   60                                 17    98.95    0.05     1.00   15     6    62                                 18    98.90    0.10     1.00   10     5    61                                 19    98.00    1.00     1.00   25     8    60                                 20    95.00    4.00     1.00   54     15   59                                 21    97.99    0.01     2.00   60     18   51                                 22    97.95    0.05     2.00   25     8    51                                 23    97.90    0.10     2.00   17     7    52                                 24    97.00    1.00     2.00   43     12   51                                 25    94.00    4.00     2.00   94     30   50                                 ______________________________________                                    

EXAMPLE 10

Ceramic discs were fabricated from SrTiO₃ as the first ingredient, Y₂ O₃as the second ingredient, and MoO₃ as the third ingredient, in variouscombinations of proportions, and were processed into varistors, throughexactly the same procedure as in EXAMPLE 1. TABLE 10 lists theproportions of the above three ingredients, together with the E₁₀, α,and C of the varistors made therefrom, as measured by the same method asin EXAMPLE 1.

                  TABLE 10                                                        ______________________________________                                        Test  Composition in percent                                                                           Properties                                           No.   SrTiO.sub.3                                                                            Y.sub.2 O.sub.3                                                                        MoO.sub.3                                                                            E.sub.10, V                                                                          α                                                                            C, nF                              ______________________________________                                        1     99.98    0.01     0.01   8      5    42                                 2     99.94    0.05     0.01   3      4    50                                 3     99.89    0.10     0.01   2      4    61                                 4     98.99    1.00     0.01   5      4    52                                 5     95.99    4.00     0.01   12     6    46                                 6     99.94    0.01     0.05   12     6    46                                 7     99.90    0.05     0.05   4      4    63                                 8     99.85    0.10     0.05   3      4    74                                 9     98.95    1.00     0.05   7      5    66                                 10    95.95    4.00     0.05   18     7    52                                 11    99.89    0.01     0.10   18     7    41                                 12    99.85    0.05     0.10   7      5    51                                 13    99.80    0.10     0.10   5      4    63                                 14    98.90    1.00     0.10   11     6    57                                 15    95.90    4.00     0.10   25     8    41                                 16    98.99    0.01     1.00   38     11   33                                 17    98.95    0.05     1.00   15     7    49                                 18    98.90    0.10     1.00   9      6    61                                 19    98.00    1.00     1.00   24     8    41                                 20    95.00    4.00     1.00   57     16   36                                 21    94.99    0.01     5.00   70     21   19                                 22    94.95    0.05     5.00   27     8    32                                 23    94.90    0.10     5.00   17     7    43                                 24    94.00    1.00     5.00   43     13   33                                 25    91.00    4.00     5.00   99     29   21                                 ______________________________________                                    

EXAMPLE 11

This EXAMPLE is intended for the confirmation of the fact that the useof two different metal oxides as the second set of ingredients, incombination with the first and third ingredients chosen in accordancewith the invention, makes the resulting ceramic materials as suitablefor varistors as those containing but one second ingredient. Thefollowing combinations of two different metal oxides were tested as thesecond sets of ingredients, together with SrTiO₃ as the first ingredientand CuO as the third ingredient: Nb₂ O₅ and Ta₂ O₅, Nb₂ O₅ and WO₃, Nb₂O₅ and La₂ O₃, Nb₂ O₅ and CeO₂, Nb₂ O₅ and Dy₂ O₃, La₂ O₅ and Ta₂ O₅,La₂ O₃ and WO₃, La₂ O₃ and CeO₂, La₂ O₃ and Nd₂ O₃, and La₂ O₃ and Sm₂O₃.

Ceramic discs were fabricated from the combinations of the aboveenumerated components, in various sets of proportions, and wereprocessed into varistors, through exactly the same procedure as inEXAMPLE 1. TABLES 11A through 11J represent the proportions of therespective combinations of components, as well as the E₁₀, α, and C ofthe varistors prepared therefrom, as measured by the same method as inEXAMPLE 1. It will be noted from these tables that the ceramiccompositions of this EXAMPLE 11 are as suitable for varistors as thoseof EXAMPLES 1 through 10.

                  TABLE 11A                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      Ta.sub.2 O.sub.5                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.4    0.02    0.08  0.5   12    5    71                               2     99.4    0.05    0.05  0.5   13    6    68                               3     99.4    0.08    0.02  0.5   13    6    67                               ______________________________________                                    

                  TABLE 11B                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      WO.sub.3                                                                            CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        4     99.4    0.02    0.08  0.5   14    6    66                               5     99.4    0.05    0.05  0.5   13    6    65                               6     99.4    0.08    0.02  0.5   14    6    67                               ______________________________________                                    

                  TABLE 11C                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      La.sub.2 O.sub.3                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        7     99.4    0.02    0.08  0.5   9     5    79                               8     99.4    0.05    0.05  0.5   8     5    83                               9     99.4    0.08    0.02  0.5   8     5    86                               ______________________________________                                    

                  TABLE 11D                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CeO.sub.2                                                                           CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        10    99.4    0.02    0.08  0.5   7     5    89                               11    99.4    0.05    0.05  0.5   8     5    91                               12    99.4    0.08    0.02  0.5   7     5    90                               ______________________________________                                    

                  TABLE 11E                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      Dy.sub.2 O.sub.3                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        13    99.4    0.02    0.08  0.5   7     5    87                               14    99.4    0.05    0.05  0.5   7     5    89                               15    99.4    0.08    0.02  0.5   6     4    93                               ______________________________________                                    

                  TABLE 11F                                                       ______________________________________                                         Test Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      Ta.sub.2 O.sub.5                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        16    99.4    0.02    0.08  0.5   10    5    76                               17    99.4    0.05    0.05  0.5   11    5    73                               18    99.4    0.08    0.02  0.5   10    5    77                               ______________________________________                                    

                  TABLE 11G                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      WO.sub.3                                                                            CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        19    99.4    0.02    0.08  0.5   11    5    70                               20    99.4    0.05    0.05  0.5   12    5    65                               21    99.4    0.08    0.02  0.5   10    5    74                               ______________________________________                                    

                  TABLE 11H                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      CeO.sub.2                                                                           CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        22    99.4    0.02    0.08  0.5   7     4    84                               23    99.4    0.05    0.05  0.5   7     5    83                               24    99.4    0.08    0.02  0.5   8     5    79                               ______________________________________                                    

                  TABLE 11I                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      Nd.sub.2 O.sub.3                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        25    99.4    0.02    0.08  0.5   6     4    92                               26    99.4    0.05    0.05  0.5   7     4    86                               27    99.4    0.08    0.02  0.5   7     4    83                               ______________________________________                                    

                  TABLE 11J                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      Sm.sub.2 O.sub.3                                                                    CuO   E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        28    99.4    0.02    0.08  0.5   8     5    83                               29    99.4    0.05    0.05  0.5   7     4    90                               30    99.4    0.08    0.02  0.5   7     5    87                               ______________________________________                                    

EXAMPLE 12

This EXAMPLE is intended to prove that ceramic materials suitable forvaristors can be fabricated with the use of two different metal oxidesas the third set of ingredients, in combination with the first andsecond ingredients chosen in accordance with the invention. Thefollowing combinations of two different metal oxides were tested as thesecond sets of ingredients, together with SrTiO₃ as the first ingredientand Nb₂ O₅, WO₃ or La₂ O₃ as the second ingredient: CuO and Cu₂ O, CuOand MoO₃, MoO₃ and V₂ O₅, V₂ O₅ and CrO₃, and CrO₃ and Cu₂ O.

Ceramic bodies were fabricated from the various combinations of four ofthe listed ingredients, in various sets of proportions, and wereprocessed into varistors, through exactly the same procedure as inEXAMPLE 1. TABLES 12A through 12-O represent the proportions of suchcombinations of ingredients, as well as the E₁₀, α, and C of thevaristors prepared therefrom, as measured by the same method as inEXAMPLE 1. The tabulated results indicate that the ceramic compositionof this EXAMPLE 12 are as suitable for varistors as those of EXAMPLES 1through 10.

                  TABLE 12A                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CuO   Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.4    0.1     0.1   0.4   11    5    69                               2     99.4    0.1     0.25  0.25  10    5    72                               3     99.4    0.1     0.4   0.1   11    5    68                               ______________________________________                                    

                  TABLE 12B                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CuO   MoO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        4     99.4    0.1     0.1   0.4   12    5    68                               5     99.4    0.1     0.25  0.25  11    5    70                               6     99.4    0.1     0.4   0.1   10    5    73                               ______________________________________                                    

                  TABLE 12C                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      MoO.sub.3                                                                           V.sub.2 O.sub.5                                                                     E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        7     99.4    0.1     0.1   0.4   13    5    62                               8     99.4    0.1     0.25  0.25  15    6    59                               9     99.4    0.1     0.4   0.1   15    6    59                               ______________________________________                                    

                  TABLE 12D                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      V.sub.2 O.sub.5                                                                     CrO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        10    99.4    0.1     0.1   0.4   15    6    60                               11    99.4    0.1     0.25  0.25  14    5    62                               12    99.4    0.1     0.4   0.1   13    5    67                               ______________________________________                                    

                  TABLE 12E                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CrO.sub.3                                                                           Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        13    99.4    0.1     0.1   0.4   10    5    72                               14    99.4    0.1     0.25  0.25   9    5    76                               15    99.4    0.1     0.4   0.1   12    5    67                               ______________________________________                                    

                  TABLE 12F                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           WO.sub.3                                                                              CuO   Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        16    99.4    0.1     0.1   0.4   12    5    65                               17    99.4    0.1     0.25  0.25  13    6    62                               18    99.4    0.1     0.4   0.1   13    5    63                               ______________________________________                                    

                  TABLE 12G                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           WO.sub.3                                                                              CuO   MoO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        19    99.4    0.1     0.1   0.4   13    5    62                               20    99.4    0.1     0.25  0.25  15    5    59                               21    99.4    0.1     0.4   0.1   15    6    57                               ______________________________________                                    

                  TABLE 12H                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           WO.sub.3                                                                              MoO.sub.3                                                                           V.sub.2 O.sub.5                                                                     E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        22    99.4    0.1     0.1   0.4   14    5    60                               23    99.4    0.1     0.25  0.25  16    6    55                               24    99.4    0.1     0.4   0.1   15    6    59                               ______________________________________                                    

                  TABLE 12I                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           WO.sub.3                                                                              V.sub.2 O.sub.5                                                                     CrO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        25    99.4    0.1     0.1   0.4   16    6    55                               26    99.4    0.1     0.25  0.25  16    6    54                               27    99.4    0.1     0.4   0.1   13    5    62                               ______________________________________                                    

                  TABLE 12J                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           WO.sub.3                                                                              CrO.sub.3                                                                           Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        28    99.4    0.1     0.1   0.4   10    5    71                               29    99.4    0.1     0.25  0.25  12    5    66                               30    99.4    0.1     0.4   0.1   12    5    65                               ______________________________________                                    

                  TABLE 12K                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      CuO   Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        31    99.4    0.1     0.1   0.4   8     5    77                               32    99.4    0.1     0.25  0.25  7     5    81                               33    99.4    0.1     0.4   0.1   7     5    82                               ______________________________________                                    

                  TABLE 12L                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      CuO   MoO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        34    99.4    0.1     0.1   0.4   7     5    82                               35    99.4    0.1     0.25  0.25  7     5    83                               36    99.4    0.1     0.4   0.1   8     5    80                               ______________________________________                                    

                  TABLE 12M                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      MoO.sub.3                                                                           V.sub.2 O.sub.5                                                                     E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        37    99.4    0.1     0.1   0.4   9     5    76                               38    99.4    0.1     0.25  0.25  9     5    72                               39    99.4    0.1     0.4   0.1   10    5    69                               ______________________________________                                    

                  TABLE 12N                                                       ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      V.sub.2 O.sub.5                                                                     CrO.sub.3                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        40    99.4    0.1     0.1   0.4   10    5    68                               41    99.4    0.1     0.25  0.25  9     5    72                               42    99.4    0.1     0.4   0.1   8     5    81                               ______________________________________                                    

                  TABLE 12-O                                                      ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           La.sub.2 O.sub.3                                                                      CrO.sub.3                                                                           Cu.sub.2 O                                                                          E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        43    99.4    0.1     0.1   0.4   7     4    82                               44    99.4    0.1     0.25  0.25  6     4    85                               45    99.4    0.1     0.4   0.1   7     5    83                               ______________________________________                                    

EXAMPLE 13

In order to ascertain the relationship between the temperatures of theoxidative heat treatment during the fabrication of ceramic materials andthe properties of the varistors made therefrom, the temperature of theoxidative heat treatment was set in this EXAMPLE at various values from700° to 1170° C. Ceramic bodies were fabricated from the combinations ofSrTiO₃, Nb₂ O₅ and CuO, of SrTiO₃, Dy₂ O₃ and Cu₂ O, of SrTiO₃, CeO andV₂ O₅, of SrTiO₃, WO₃ and CrO₃, of SrTiO₃, Y₂ O₃ and MoO₃, and ofSrTiO₃, Ta₂ O₅ and MnO₂, in various sets of proportions, and wereprocessed into varistors in a manner identical in other respects withthat of EXAMPLE 1. TABLES 13A through 13F give the proportions of suchcombinations of ingredients, as well as the temperatures of theoxidative heat treatment, the resistivities of the ceramic bodies, andof the varistors made therefrom. The resistivity was measured by thefour-probe method at a temperature of 25° C.

                  TABLE 13A                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Composition in percent                                                                        oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CuO   treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                        1    99.0    0.5     0.5    700      .sup. 5 × 10.sup.-1                                                              1                               2    99.0    0.5     0.5    800      3 × 10.sup.                                                                      2                               3    99.0    0.5     0.5    900      1 × 10.sup.3                                                                     4                               4    99.0    0.5     0.5   1000      5 × 10.sup.3                                                                    13                               5    99.0    0.5     0.5   1100      8 × 10.sup.3                                                                    26                               6    99.0    0.5     0.5   1170      2 × 10.sup.4                                                                    61                               ______________________________________                                    

                  TABLE 13B                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Composition in percent                                                                        oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           Dy.sub.2 O.sub.3                                                                      Cu.sub.2 O                                                                          treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                         7   99.0    0.5     0.5    700      .sup. 6 × 10.sup.-1                                                              1                                8   99.0    0.5     0.5    800      4 × 10.sup.                                                                      2                                9   99.0    0.5     0.5    900      1 × 10.sup.3                                                                     4                               10   99.0    0.5     0.5   1000      5 × 10.sup.3                                                                    12                               11   99.0    0.5     0.5   1100      9 × 10.sup.3                                                                    29                               12   99.0    0.5     0.5   1170      3 × 10.sup.4                                                                    69                               ______________________________________                                    

                  TABLE 13C                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Position in percent                                                                           oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           CeO.sub.2                                                                             V.sub.2 O.sub.5                                                                     treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                        13   99.0    0.5     0.5    700      .sup. 8 × 10.sup.-1                                                              1                               14   99.0    0.5     0.5    800      6 × 10.sup.                                                                      2                               15   99.0    0.5     0.5    900      2 × 10.sup.3                                                                     4                               16   99.0    0.5     0.5   1000      7 × 10.sup.3                                                                    15                               17   99.0    0.5     0.5   1100      10 × 10.sup.3                                                                   31                               18   99.0    0.5     0.5   1170      5 × 10.sup.4                                                                    84                               ______________________________________                                    

                  TABLE 13D                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Composition in percent                                                                        oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           WO.sub.3                                                                              CrO.sub.3                                                                           treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                        19   99.0    0.5     0.5    700      .sup. 6 × 10.sup.-1                                                              1                               20   99.0    0.5     0.5    800      6 × 10.sup.                                                                      2                               21   99.0    0.5     0.5    900      1 × 10.sup.3                                                                     4                               22   99.0    0.5     0.5   1000      6 × 10.sup.3                                                                    13                               23   99.0    0.5     0.5   1100      8 × 10.sup.3                                                                    30                               24   99.0    0.5     0.5   1170      3 × 10.sup.4                                                                    70                               ______________________________________                                    

                  TABLE 13E                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Composition in percent                                                                        oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           Y.sub.2 O.sub.3                                                                       MoO.sub.3                                                                           treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                        25   99.0    0.5     0.5    700      .sup. 7 × 10.sup.-1                                                              1                               26   99.0    0.5     0.5    800      7 × 10.sup.                                                                      2                               27   99.0    0.5     0.5    900      2 × 10.sup.3                                                                     4                               28   99.0    0.5     0.5   1000      7 × 10.sup.3                                                                    16                               29   99.0    0.5     0.5   1100      11 × 10.sup.3                                                                   33                               30   99.0    0.5     0.5   1170      5 × 10.sup.4                                                                    86                               ______________________________________                                    

                  TABLE 13F                                                       ______________________________________                                                       Temperature of                                                                          Properties                                           Test Composition in percent                                                                        oxidative heat                                                                            Resistivity,                                 No.  SrTiO.sub.3                                                                           Ta.sub.2 O.sub.5                                                                      MnO.sub.2                                                                           treatment, °C.                                                                   ohm-cm  α                          ______________________________________                                        31   99.0    0.5     0.5    700      .sup. 6 × 10.sup.-1                                                              1                               32   99.0    0.5     0.5    800      4 × 10.sup.                                                                      2                               33   99.0    0.5     0.5    900      1 × 10.sup.3                                                                     4                               34   99.0    0.5     0.5   1000      6 × 10.sup.3                                                                    12                               35   99.0    0.5     0.5   1100      9 × 10.sup.3                                                                    31                               36   99.0    0.5     0.5   1170      3 × 10.sup.4                                                                    63                               ______________________________________                                    

On the basis of the data given in TABLE 13A, FIG. 6 plots the curve ofthe α of the SrTiO₃ --Nb₂ O₅ --CuO varistors against the temperature ofthe oxidative heat treatment. This graph makes clear that the α of thevaristors can be controlled by the temperature of the oxidative heattreatment during the fabrication of the ceramic bodies. It will also beseen from TABLES 13A through 13F that the resistivity of the ceramicbodies varies with the temperature of the oxidative heat treatment. Forthe provision of varistors of the desired characteristics, therefore,the oxidative heat treatment should be conducted in a temperature rangeof about 800°-1170° C. Should the temperature be less than about 800°C., the α of the ceramic bodies would become too small for varistors. Ifthe temperature were made higher than about 1300° C., on the other hand,then the resistivity of the ceramic bodies would become too high forvaristors.

EXAMPLE 14

Ceramic discs were fabricated from various combinations of threepossible ingredients set forth in TABLE 14, in like proportions, andwere processed into varistors, through a procedure similar to that ofEXAMPLE 1. In order to evaluate the pulse-withstanding abilities ofthese varistors, 10 voltage pulses of 100 V were successively applied toeach varistor, and a rate of change in E₁₀ before and after the pulseapplication was calculated. TABLE 14 summarizes the results.

                  TABLE 14                                                        ______________________________________                                        Composition                                                                         First      Second     Third    Rate of                                  Test  ingredient ingredient ingredient                                                                             change in                                No.   99.4%      0.1%       0.5%     E.sub.10, %                              ______________________________________                                        1     SrTiO.sub.3                                                                              Nb.sub.2 O.sub.5                                                                         CuO      0.03                                     2     SrTiO.sub.3                                                                              WO.sub.3   CrO.sub.3                                                                              0.02                                     3     SrTiO.sub.3                                                                              Ta.sub.2 O.sub.5                                                                         MnO.sub.2                                                                              0.03                                     4     SrTiO.sub.3                                                                              Y.sub.2 O.sub.3                                                                          MoO.sub.3                                                                              0.06                                     5     SrTiO.sub.3                                                                              Sm.sub.2 O.sub.3                                                                         CuO      0.04                                     6     SrTiO.sub.3                                                                              CeO.sub.2  V.sub.2 O.sub.5                                                                        0.04                                     7     SrTiO.sub.3                                                                              Pr.sub.6 O.sub.11                                                                        MnO.sub.2                                                                              0.06                                     8     SrTiO.sub.3                                                                              Nd.sub.2 O.sub.3                                                                         CrO.sub.3                                                                              0.05                                     9     SrTiO.sub.3                                                                              Dy.sub.2 O.sub.3                                                                         Cu.sub.2 O                                                                             0.05                                     10    SrTiO.sub.3                                                                              La.sub.2 O.sub.3                                                                         MoO.sub.3                                                                              0.06                                     ______________________________________                                    

It will be observed from TABLE 14 that the E₁₀ of the various varistorsin accordance with the invention varies only from 0.02 to 0.06% beforeand after the application of ten 100-volt pulses in succession. The rateof change in E₁₀ of the conventional ZnO varistors, measured by a likemethod by way of comparison, was in the range of 15-20%. The littlechange in E₁₀ of the varistors in accordance with the inventionevidences that they hardly suffer from voltage surges in use.

The above presented EXAMPLES 1 through 14 prove that the secondingredient should be used in a proportion of about 0.001-5.000% in anycombination with first and second ingredients in the manufacture ofceramic materials in accordance with the invention. Intended as anadditive for making the materials semiconductive, the second ingredientwhen used in that range makes the size of the crystal grains from about20 to 40 micrometers in diameter and does not make the E₁₀ too high.Should the content of the second ingredient fall outside the specifiedrange, the grain size would become too large, and the E₁₀ too high, toprovide favorable semiconductor materials and favorable varistors. Theproportion of the second ingredient should be in a range of 0.05-1.00%to obtain appropriate values of E₁₀.

Intended as an additive for improving the nonlinear volt-amperecharacteristic of the ceramic materials, the third ingredient should beused in an amount ranging from about 0.01 to about 5.00%. If the contentof the third ingredient were less than about 0.01%, the E₁₀, α, etc., ofceramic bodies would fluctuate considerably, making it difficult toprovide varistors of desired performance characteristics. If it weregreater than about 5.00%, on the other hand, then the resistive oxideregion 5, in FIG. 1, of each ceramic body would occupy too large a spacein relation to the crystal grains 4, and the third ingredient at thesurfaces of the ceramic bodies would cause their mutual adhesion duringfiring or would flow over the surfaces. Too great a proportion of thethird ingredient would also result in an unduly high value of E₁₀. Apreferred range of the proportion of the third ingredient is from about0.05 to about 1.00%.

EXAMPLE 15

While all the foregoing EXAMPLES dealt with the ceramic compositions ofthe first, second and third ingredients, the present EXAMPLE introducesa fourth ingredient with a view to the higher coherency of the ceramicbodies. The particular fourth ingredient herein employed was GeO₂, incombination with SrTiO₃ as the first ingredient, Nb₂ O₅ as the secondingredient, and CuO as the third ingredient, and in various sets ofproportions presented in TABLE 15. These ingredients were processed intoceramic discs, and further into varistors, through the same procedure asin EXAMPLE 1 except that GeO₂ was used as the fourth ingredient and thatthe oxidative heat treatment of the fired bodies was performed at atemperature of 1000° C. TABLE 15 also indicates the E₁₀, α, and C of thevaristors manufactured as above.

As is apparent from the tabulated results, the varistors containing thefourth ingredient have properties similar to those of the varistorshaving no fourth ingredient. The addition of GeO₂ as the fourthingredient, however, made more uniform the size of the ceramicparticles, which ranged from 20 to 40 micrometers, thereby serving toreduce fluctuations in the E₁₀ and α of the varistors.

                  TABLE 15                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CuO   GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   8     5    101                              2     99.44   0.05    0.01  0.5   3     4    107                              3     99.39   0.10    0.01  0.5   2     4    120                              4     98.49   1.00    0.01  0.5   6     5    101                              5     96.99   2.50    0.01  0.5   11    5    96                               6     99.44   0.01    0.05  0.5   9     5    97                               7     99.40   0.05    0.05  0.5   3     4    101                              8     99.35   0.10    0.05  0.5   2     4    116                              9     98.45   1.00    0.05  0.5   7     5    99                               10    96.95   2.50    0.05  0.5   12    5    95                               11    99.39   0.01    0.10  0.5   10    6    89                               12    99.35   0.05    0.10  0.5   4     4    100                              13    99.30   0.10    0.10  0.5   3     4    117                              14    98.40   1.00    0.10  0.5   8     6    92                               15    96.90   2.50    0.10  0.5   14    7    86                               16    98.49   0.01    1.00  0.5   18    8    82                               17    98.45   0.05    1.00  0.5   10    6    92                               18    98.40   0.10    1.00  0.5   7     6    105                              19    97.50   1.00    1.00  0.5   14    8    85                               20    96.00   2.50    1.00  0.5   33    11   61                               21    94.49   0.01    5.00  0.5   35    12   66                               22    94.45   0.05    5.00  0.5   24    9    79                               23    94.40   0.10    5.00  0.5   16    8    91                               24    93.50   1.00    5.00  0.5   26    10   76                               25    92.00   2.50    5.00  0.5   89    32   33                               ______________________________________                                    

EXAMPLE 16

SrTiO₃ as the first ingredient was combined with Nb₂ O₅ as the secondingredient, Cu₂ O as the third ingredient, and GeO₂ as the fourthingredient. In various sets of proportions these ingredients wereprocessed into ceramic discs, and further into varistors, through thesame procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. TABLE 16 lists the proportions ofthe above four ingredients, together with the E₁₀, α, and C of thevaristors made therefrom, as measured by the same method as in EXAMPLE1.

                  TABLE 16                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      Cu.sub.2 O.sub.5                                                                    GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   9     4    76                               2     99.44   0.05    0.01  0.5   4     4    87                               3     99.39   0.10    0.01  0.5   2     4    98                               4     98.49   1.00    0.01  0.5   5     4    86                               5     96.99   2.50    0.01  0.5   14    6    71                               6     99.44   0.01    0.05  0.5   10    5    75                               7     99.40   0.05    0.05  0.5   4     4    83                               8     99.35   0.10    0.05  0.5   2     4    100                              9     98.45   1.00    0.05  0.5   6     4    81                               10    96.95   2.50    0.05  0.5   16    7    73                               11    99.39   0.01    0.10  0.5   12    6    72                               12    99.35   0.05    0.10  0.5   5     5    81                               13    99.30   0.10    0.10  0.5   3     4    92                               14    98.40   1.00    0.10  0.5   6     4    82                               15    96.90   2.50    0.10  0.5   17    8    62                               16    98.49   0.01    1.00  0.5   33    11   61                               17    98.45   0.05    1.00  0.5   14    7    74                               18    98.40   0.10    1.00  0.5   7     5    82                               19    97.50   1.00    1.00  0.5   18    8    63                               20    96.00   2.50    1.00  0.5   49    15   43                               21    96.99   0.01    2.50  0.5   65    21   36                               22    96.95   0.05    2.50  0.5   29    10   51                               23    96.90   0.10    2.50  0.5   15    7    77                               24    96.00   1.00    2.50  0.5   36    10   51                               25    94.50   2.50    2.50  0.5   95    34   39                               ______________________________________                                    

EXAMPLE 17

SrTiO₃ as the first ingredient was combined with Nb₂ O₅ as the secondingredient, V₂ O₅ as the third ingredient, and GeO₂ as the fourthingredient. In various sets of of proportions these ingredients wereprocessed into ceramic disc, and further into varistors, through thesame procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. TABLE 17 lists the proportions ofthe above four ingredients, together with the E₁₀, α, and C of thevaristors made therefrom, as measured by the same method as in EXAMPLE1.

                  TABLE 17                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      V.sub.2 O.sub.5                                                                     GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   4     4    88                               2     99.44   0.05    0.01  0.5   2     4    93                               3     99.39   0.10    0.01  0.5   2     4    91                               4     98.49   1.00    0.01  0.5   4     4    87                               5     96.99   2.50    0.01  0.5   8     5    72                               6     99.44   0.01    0.05  0.5   5     4    83                               7     99.40   0.05    0.05  0.5   3     4    82                               8     99.35   0.10    0.05  0.5   2     4    89                               9     98.45   1.00    0.05  0.5   5     4    79                               10    96.95   2.50    0.05  0.5   10    5    63                               11    99.39   0.01    0.1   0.5   6     5    81                               12    99.35   0.05    0.1   0.5   3     4    80                               13    99.30   0.10    0.1   0.5   3     4    81                               14    98.40   1.00    0.1   0.5   7     4    66                               15    96.90   2.50    0.1   0.5   13    6    51                               16    98.99   0.01    0.50  0.5   12    6    70                               17    98.95   0.05    0.50  0.5   6     4    76                               18    98.90   0.10    0.50  0.5   5     4    82                               19    98.00   1.00    0.50  0.5   13    6    49                               20    96.50   2.50    0.50  0.5   25    8    42                               21    98.49   0.01    1.00  0.5   17    8    50                               22    98.45   0.05    1.00  0.5   9     5    75                               23    98.40   0.10    1.00  0.5   7     4    80                               24    97.50   1.00    1.00  0.5   19    8    44                               25    96.00   2.50    1.00  0.5   38    13   26                               ______________________________________                                    

EXAMPLE 18

SrTiO₃ as the first ingredient was combined with Nb₂ O₅ as the secondingredient, CrO₃ as the third ingredient, and GeO₂ as the fourthingredient. In various sets of proportions these ingredients wereprocessed into ceramic discs, and further into varistors, through thesame procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. TABLE 18 lists the proportions ofthe above four ingredients, together with the E₁₀, α, and C of thevaristors made therefrom, as measured by the same method as in EXAMPLE1.

                  TABLE 18                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      CrO.sub.3                                                                           GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   8     5    61                               2     99.44   0.05    0.01  0.5   3     4    77                               3     99.39   0.10    0.01  0.5   2     4    76                               4     98.49   1.00    0.01  0.5   7     5    60                               5     96.99   2.50    0.01  0.5   14    6    52                               6     99.44   0.01    0.05  0.5   9     5    60                               7     99.40   0.05    0.05  0.5   3     4    76                               8     99.35   0.10    0.05  0.5   2     4    71                               9     98.45   1.00    0.05  0.5   8     5    61                               10    96.95   2.50    0.05  0.5   15    7    50                               11    99.39   0.01    0.10  0.5   10    6    61                               12    99.35   0.05    0.10  0.5   4     4    72                               13    99.30   0.10    0.10  0.5   3     4    73                               14    98.40   1.00    0.10  0.5   9     6    52                               15    96.90   2.50    0.10  0.5   18    7    43                               16    98.49   0.01    1.00  0.5   32    11   35                               17    98.45   0.05    1.00  0.5   12    5    62                               18    98.40   0.10    1.00  0.5   8     5    64                               19    97.50   1.00    1.00  0.5   28    10   36                               20    96.00   2.50    1.00  0.5   57    17   32                               21    97.49   0.01    2.00  0.5   48    15   28                               22    97.45   0.05    2.00  0.5   18    7    42                               23    97.40   0.10    2.00  0.5   12    6    61                               24    96.50   1.00    2.00  0.5   45    14   29                               25    95.00   2.50    2.00  0.5   91    33   21                               ______________________________________                                    

EXAMPLE 19

SrTiO₃ as the first ingredient was combined with Nb₂ O₅ as the secondingredient, MoO₃ as the third ingredient, and GeO₂ as the fourthingredient. In various sets of proportions these ingredients wereprocessed into ceramic discs, and further into varistors, through thesame procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. TABLE 19 lists the proportions ofthe above four ingredients, together with the E₁₀, α, and C of thevaristors made therefrom, as measured by the same method as in EXAMPLE1.

                  TABLE 19                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      MoO.sub.3                                                                           GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   5     4    131                              2     99.44   0.05    0.01  0.5   3     4    143                              3     99.39   0.10    0.01  0.5   2     4    154                              4     98.49   1.00    0.01  0.5   5     4    130                              5     96.99   2.50    0.01  0.5   12    6    110                              6     99.44   0.01    0.05  0.5   7     5    123                              7     99.40   0.05    0.05  0.5   3     4    145                              8     99.35   0.10    0.05  0.5   2     4    161                              9     98.45   1.00    0.05  0.5   6     5    129                              10    96.95   2.50    0.05  0.5   14    7    105                              11    99.39   0.01    0.10  0.5   8     5    116                              12    99.35   0.05    0.10  0.5   4     4    139                              13    99.30   0.10    0.10  0.5   3     4    144                              14    98.40   1.00    0.10  0.5   7     6    121                              15    96.90   2.50    0.10  0.5   16    8    101                              16    98.49   0.01    1.00  0.5   21    9     93                              17    98.45   0.05    1.00  0.5   11    6    106                              18    98.40   0.10    1.00  0.5   5     4    137                              19    97.50   1.00    1.00  0.5   18    8     99                              20    96.00   2.50    1.00  0.5   42    14    63                              21    94.49   0.01    5.00  0.5   39    12    72                              22    94.45   0.05    5.00  0.5   20    9     96                              23    94.40   0.10    5.00  0.5   13    7    106                              24    93.50   1.00    5.00  0.5   33    11    79                              25    92.00   2.50    5.00  0.5   78    27    46                              ______________________________________                                    

EXAMPLE 20

SrTiO₃ as the first ingredient was combined with Nb₂ O₅ as the secondingredient, MnO₂ as the third ingredient, and GeO₂ as the fourthingredient. In various sets of proportions these ingredients wereprocessed into ceramic discs, and further into varistors, through thesame procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. TABLE 20 lists the proportions ofthe above four ingredients, together with the E₁₀, α, and C of thevaristors made therefrom, as measured by the same method as in EXAMPLE1.

                  TABLE 20                                                        ______________________________________                                        Test  Composition in percent                                                                            Properties                                          No.   SrTiO.sub.3                                                                           Nb.sub.2 O.sub.5                                                                      MnO.sub.2                                                                           GeO.sub.2                                                                           E.sub.10, V                                                                         α                                                                            C, nF                            ______________________________________                                        1     99.48   0.01    0.01  0.5   9     5    121                              2     99.44   0.05    0.01  0.5   5     4    130                              3     99.39   0.10    0.01  0.5   2     4    141                              4     98.49   1.00    0.01  0.5   6     5    125                              5     96.99   2.50    0.01  0.5   11    5    115                              6     99.44   0.01    0.05  0.5   12    6    109                              7     99.40   0.05    0.05  0.5   6     4    123                              8     99.35   0.10    0.05  0.5   3     4    135                              9     98.45   1.00    0.05  0.5   8     5    115                              10    96.95   2.50    0.05  0.5   13    6    105                              11    99.39   0.01    0.10  0.5   14    7    103                              12    99.35   0.05    0.10  0.5   8     5    113                              13    99.30   0.10    0.10  0.5   3     4    139                              14    98.40   1.00    0.10  0.5   10    5    110                              15    96.90   2.50    0.10  0.5   18    7     96                              16    98.49   0.01    1.00  0.5   42    15    71                              17    98.45   0.05    1.00  0.5   24    8     89                              18    98.40   0.10    1.00  0.5   9     5    120                              19    97.50   1.00    1.00  0.5   28    10    89                              20    96.00   2.50    1.00  0.5   52    19    66                              21    96.99   0.01    2.50  0.5   72    30    48                              22    96.95   0.05    2.50  0.5   41    14    62                              23    96.90   0.10    2.50  0.5   17    7     96                              24    96.00   1.00    2.50  0.5   47    16    59                              25    94.50   2.50    2.50  0.5   90    36    33                              ______________________________________                                    

EXAMPLE 21

SrTiO₃ as the first ingredient and CuO as the third ingredient werevariously combined with a second ingredient selected from the group ofTa₂ O₅, WO₃, La₂ O₃, Dy₂ O₃, Y₂ O₃, CeO₂, Nb₂ O₅, Pr₆ O₁₁, Nd₂ O₃, andSm₂ O₃, and with a fourth ingredient selected from the group of B₂ O₃,ZnO, PbO, and GeO₂. This EXAMPLE was intended to prove that B₂ O₃, ZnOand PbO could each be used as the fourth ingredient, in place of GeO₂tested in some foregoing EXAMPLES. It was also intended to ascertain theallowable range of percentages in which the fourth ingredient might beused to provide ceramic materials suitable for varistors.

Various combinations of four selected ingredients, each in various setsof proportions, were processed into ceramic discs through the sameprocedure as in EXAMPLE 1 except that the temperature of the oxidativeheat treatment was 1000° C. TABLES 21A through 21S represent the variouscombinations and proportions of the above ingredients, as well as theresistivities of the corresponding ceramic bodies, as measured by thefour-probe method.

The resistivity of each ceramic body serves as a measure of its utilityas a semiconductor. Conventional SrTiO₃ ceramic materials, for use incapacitors, had a resistivity of more than 10¹⁰ ohm-cm in general.Contrastively, as will be noted from TABLES 21A through 21S, the ceramicbodies of this invention have all a resistivity of less than 10⁶ ohm-cmand thus are sufficiently semiconductive and suitable for varistors.

Experiment has also proved that if the content of the fourth ingredientin each composition is less than about 0.01%, it hardly serves thepurpose of improving the coherency of the ceramic bodies preparedtherefrom. Should the proportion of the fourth ingredient exceed about4.00%, on the other hand, the resistivity of the ceramic bodies willbecome too high, making them unsuitable for varistors. Thus theproportion of the fourth ingredient should range from about 0.01 toabout 4.00%, preferably from about 0.5 to about 1.0%.

                  TABLE 21A                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Ta.sub.2 O.sub.5                                                                       CuO    B.sub.2 O.sub.3                                                                      ohm-cm                                  ______________________________________                                        1     99.485   0.005    0.5    0.01   6 × 10.sup.-1                     2     98.995   0.005    0.5    0.50   13 × 10.sup.-1                    3     95.495   0.005    0.5    4.00   19 × 10.sup.-1                    4     98.99    0.50     0.5    0.01   2 × 10.sup.-1                     5     98.50    0.50     0.5    0.50   5 × 10.sup.-1                     6     95.00    0.50     0.5    4.00   7 × 10.sup.-1                     7     96.99    2.50     0.5    0.01   9 × 10.sup.-1                     8     96.50    2.50     0.5    0.50   20 × 10.sup.-1                    9     93.00    2.50     0.5    4.00   31 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21B                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            WO.sub.3 CuO    B.sub.2 O.sub.3                                                                      ohm-cm                                  ______________________________________                                        10    99.48    0.01     0.5    0.01   6 × 10.sup.-1                     11    98.99    0.01     0.5    0.50   13 × 10.sup.-1                    12    95.49    0.01     0.5    4.00   19 × 10.sup.-1                    13    98.99    0.50     0.5    0.01   2 × 10.sup.-1                     14    98.50    0.50     0.5    0.50   5 × 10.sup.-1                     15    95.00    0.50     0.5    4.00   7 × 10.sup.-1                     16    94.49    5.00     0.5    0.01   9 × 10.sup.-1                     17    94.00    5.00     0.5    0.50   20 × 10.sup.-1                    18    95.50    5.00     0.5    4.00   31 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21C                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            La.sub.2 O.sub.3                                                                       CuO    B.sub.2 O.sub.3                                                                      ohm-cm                                  ______________________________________                                        19    99.48    0.01     0.5    0.01   5 × 10.sup.-1                     20    98.99    0.01     0.5    0.50   7 × 10.sup.-1                     21    95.49    0.01     0.5    4.00   17 × 10.sup.-1                    22    98.99    0.50     0.5    0.01   2 × 10.sup.-1                     23    98.50    0.50     0.5    0.50   4 × 10.sup.-1                     24    95.00    0.50     0.5    4.00   6 × 10.sup.-1                     25    96.99    2.50     0.5    0.01   4 × 10.sup.-1                     26    96.50    2.50     0.5    0.50   6 × 10.sup.-1                     27    93.00    2.50     0.5    4.00   13 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21D                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Dy.sub.2 O.sub.3                                                                       CuO    B.sub.2 O.sub.3                                                                      ohm-cm                                  ______________________________________                                        28    99.48    0.01     0.5    0.01    7 × 10.sup.-1                    29    98.99    0.01     0.5    0.50   13 × 10.sup.-1                    30    95.49    0.01     0.5    4.00   23 × 10.sup.-1                    31    98.99    0.50     0.5    0.01    3 × 10.sup.-1                    32    98.50    0.50     0.5    0.50    5 × 10.sup.-1                    33    95.00    0.50     0.5    4.00   11 × 10.sup.-1                    34    96.99    2.50     0.5    0.01    6 × 10.sup.-1                    35    96.50    2.50     0.5    0.50   11 × 10.sup.-1                    36    93.00    2.50     0.5    4.00   20 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21E                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Y.sub.2 O.sub.3                                                                        CuO    B.sub.2 O.sub.3                                                                      ohm-cm                                  ______________________________________                                        37    99.48    0.01     0.5    0.01   7 × 10.sup.-1                     38    98.99    0.01     0.5    0.50   12 × 10.sup.-1                    39    95.49    0.01     0.5    4.00   24 × 10.sup.-1                    40    98.99    0.50     0.5    0.01   2 × 10.sup.-1                     41    98.50    0.50     0.5    0.50   3 × 10.sup.-1                     42    95.00    0.50     0.5    4.00   7 × 10.sup.-1                     43    95.49    4.00     0.5    0.01   7 × 10.sup.-1                     44    95.00    4.00     0.5    0.50   12 × 10.sup.-1                    45    91.50    4.00     0.5    4.00   25 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21F                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            CeO.sub.2                                                                              CuO    ZnO    ohm-cm                                  ______________________________________                                        46    99.48    0.01     0.5    0.01    8 × 10.sup.-1                    47    98.99    0.01     0.5    0.50   15 × 10.sup.-1                    48    95.49    0.01     0.5    4.00   33 × 10.sup.-1                    49    98.99    0.50     0.5    0.01    5 × 10.sup.-1                    50    98.50    0.50     0.5    0.50   10 × 10.sup.-1                    51    95.00    0.50     0.5    4.00   21 × 10.sup.-1                    52    95.49    4.00     0.5    0.01    9 × 10.sup.-1                    53    95.00    4.00     0.5    0.50   17 × 10.sup.-1                    54    91.50    4.00     0.5    4.00   35 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21G                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            La.sub.2 O.sub.3                                                                       CuO    ZnO    ohm-cm                                  ______________________________________                                        55    99.48    0.01     0.5    0.01    7 × 10.sup.-1                    56    98.99    0.01     0.5    0.50   13 × 10.sup.-1                    57    95.49    0.01     0.5    4.00   27 × 10.sup.-1                    58    98.99    0.50     0.5    0.01    4 × 10.sup.-1                    59    98.50    0.50     0.5    0.50    9 × 10.sup.-1                    60    95.00    0.50     0.5    4.00   16 × 10.sup.-1                    61    96.99    2.50     0.5    0.01    6 × 10.sup.-1                    62    96.50    2.50     0.5    0.50   12 × 10.sup.-1                    63    93.00    2.50     0.5    4.00   25 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21H                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            WO.sub.3 CuO    ZnO    ohm-cm                                  ______________________________________                                        64    99.48    0.01     0.5    0.01   5 × 10.sup.-1                     65    98.99    0.01     0.5    0.50   9 × 10.sup.-1                     66    95.49    0.01     0.5    4.00   20 × 10.sup.-1                    67    98.99    0.50     0.5    0.01   2 × 10.sup.-1                     68    98.50    0.50     0.5    0.50   4 × 10.sup.-1                     69    95.00    0.50     0.5    4.00   8 × 10.sup.-1                     70    94.49    5.00     0.5    0.01   4 × 10.sup.-1                     71    94.00    5.00     0.5    0.50   8 × 10.sup.-1                     72    90.50    5.00     0.5    4.00   16 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21I                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Ta.sub.2 O.sub.5                                                                       CuO    ZnO    ohm-cm                                  ______________________________________                                        73    99.485   0.005    0.5    0.01    9 × 10.sup.-1                    74    98.995   0.005    0.5    0.50   17 × 10.sup.-1                    75    95.495   0.005    0.5    4.00   36 × 10.sup.-1                    76    99.44    0.05     0.5    0.01    4 × 10.sup.-1                    77    98.95    0.05     0.5    0.50    8 × 10.sup.-1                    78    95.45    0.05     0.5    4.00   15 × 10.sup.-1                    79    96.99    2.50     0.5    0.01   13 × 10.sup.-1                    80    96.50    2.50     0.5    0.50   24 × 10.sup.-1                    81    93.00    2.50     0.5    4.00   48 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21J                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Ta.sub.2 O.sub.5                                                                       CuO    PbO    ohm-cm                                  ______________________________________                                        82    99.485   0.005    0.5    0.01    7 × 10.sup.-1                    83    98.995   0.005    0.5    0.50   15 × 10.sup.-1                    84    95.495   0.005    0.5    4.00   31 × 10.sup.-1                    85    98.99    0.50     0.5    0.01    4 × 10.sup.-1                    86    98.50    0.50     0.5    0.50    8 × 10.sup.-1                    87    95.00    0.50     0.5    4.00   18 × 10.sup.-1                    88    96.99    2.50     0.5    0.01   10 × 10.sup.-1                    89    96.50    2.50     0.5    0.50   21 × 10.sup.-1                    90    93.00    2.50     0.5    4.00   45 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21K                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       CuO    PbO    ohm-cm                                  ______________________________________                                        91    99.48    0.01     0.5    0.01   21 × 10.sup.-1                    92    98.99    0.01     0.5    0.50   44 × 10.sup.-1                    93    95.49    0.01     0.5    4.00   96 × 10.sup.-1                    94    98.99    0.50     0.5    0.01    7 × 10.sup.-1                    95    98.50    0.50     0.5    0.50   15 × 10.sup.-1                    96    95.00    0.50     0.5    4.00   30 × 10.sup.-1                    97    94.49    5.00     0.5    0.01   18 × 10.sup.-1                    98    94.00    5.00     0.5    0.50   39 × 10.sup.-1                    99    90.50    5.00     0.5    4.00   81 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21L                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Pr.sub.6 O.sub.11                                                                      CuO    PbO    ohm-cm                                  ______________________________________                                        100   99.489   0.001    0.5    0.01    8 × 10.sup.-1                    101   98.999   0.001    0.5    0.50   17 × 10.sup.-1                    102   95.499   0.001    0.5    4.00   39 × 10.sup.-1                    103   98.99    0.50     0.5    0.01    4 × 10.sup.-1                    104   98.50    0.50     0.5    0.50    9 × 10.sup.-1                    105   95.00    0.50     0.5    4.00   18 × 10.sup.-1                    106   96.99    2.50     0.5    0.01    7 × 10.sup.-1                    107   96.50    2.50     0.5    0.50   16 × 10.sup.-1                    108   93.00    2.50     0.5    4.00   32 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21M                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Nd.sub.2 O.sub.3                                                                       CuO    PbO    ohm-cm                                  ______________________________________                                        109   99.48    0.01     0.5    0.01    8 × 10.sup.-1                    110   98.99    0.01     0.5    0.50   16 × 10.sup.-1                    111   95.49    0.01     0.5    4.00   36 × 10.sup.-1                    112   98.99    0.50     0.5    0.01    3 × 10.sup.-1                    113   98.50    0.50     0.5    0.50    6 × 10.sup.-1                    114   95.00    0.50     0.5    4.00   13 × 10.sup.-1                    115   95.49    4.00     0.5    0.01    7 × 10.sup.-1                    116   95.00    4.00     0.5    0.50   15 × 10.sup.-1                    117   91.50    4.00     0.5    4.00   33 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21N                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Sm.sub.2 O.sub.3                                                                       CuO    PbO    ohm-cm                                  ______________________________________                                        118   99.48    0.01     0.5    0.01    9 × 10.sup.-1                    119   98.99    0.01     0.5    0.50   20 × 10.sup.-1                    120   95.49    0.01     0.5    4.00   41 × 10.sup.-1                    121   98.99    0.50     0.5    0.01    3 × 10.sup.-1                    122   98.50    0.50     0.5    0.50    6 × 10.sup.-1                    123   95.00    0.50     0.5    4.00   11 × 10.sup.-1                    124   96.49    3.00     0.5    0.01   10 × 10.sup.-1                    125   96.00    3.00     0.5    0.50   23 × 10.sup.-1                    126   92.50    3.00     0.5    4.00   46 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21-O                                                      ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Ta.sub.2 O.sub.5                                                                       CuO    GeO.sub.2                                                                            ohm-cm                                  ______________________________________                                        127   99.485   0.005    0.5    0.01    8 × 10.sup.-1                    128   98.995   0.005    0.5    0.50   17 × 10.sup.-1                    129   95.495   0.005    0.5    4.00   33 × 10.sup.-1                    130   98.99    0.50     0.5    0.01    4 × 10.sup.-1                    131   98.50    0.50     0.5    0.50    9 × 10.sup.-1                    132   95.00    0.50     0.5    4.00   18 × 10.sup.-1                    133   96.99    2.50     0.5    0.01   11 × 10.sup.-1                    134   96.50    2.50     0.5    0.50   25 × 10.sup.-1                    135   93.00    2.50     0.5    4.00   45 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21P                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       CuO    GeO.sub.2                                                                            ohm-cm                                  ______________________________________                                        136   99.48    0.01     0.5    0.01   29 × 10.sup.-1                    137   98.99    0.01     0.5    0.50   57 × 10.sup.-1                    138   95.49    0.01     0.5    4.00   122 × 10.sup.-1                   139   98.99    0.50     0.5    0.01   10 × 10.sup.-1                    140   98.50    0.50     0.5    0.50   24 × 10.sup.-1                    141   95.00    0.50     0.5    4.00   46 × 10.sup.-1                    142   94.49    5.00     0.5    0.01   24 × 10.sup.-1                    143   94.00    5.00     0.5    0.50   53 × 10.sup.-1                    144   90.50    5.00     0.5    4.00   103 × 10.sup.-1                   ______________________________________                                    

                  TABLE 21Q                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            CeO.sub.2                                                                              CuO    GeO.sub.2                                                                            ohm-cm                                  ______________________________________                                        145   99.48    0.01     0.5    0.01    9 × 10.sup.-1                    146   98.99    0.01     0.5    0.50   21 × 10.sup.-1                    147   95.49    0.01     0.5    4.00   40 × 10.sup.-1                    148   98.99    0.50     0.5    0.01    6 × 10.sup.-1                    149   98.50    0.50     0.5    0.50   13 × 10.sup.-1                    150   95.00    0.50     0.5    4.00   27 × 10.sup.-1                    151   95.49    4.00     0.5    0.01    8 × 10.sup.-1                    152   95.00    4.00     0.5    0.50   18 × 10.sup.-1                    153   91.50    4.00     0.5    4.00   35 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21R                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Nd.sub.2 O.sub.3                                                                       CuO    GeO.sub.2                                                                            ohm-cm                                  ______________________________________                                        154   99.48    0.01     0.5    0.01   10 × 10.sup.-1                    155   98.99    0.01     0.5    0.50   23 × 10.sup.-1                    156   95.49    0.01     0.5    4.00   46 × 10.sup.-1                    157   98.99    0.50     0.5    0.01    5 × 10.sup.-1                    158   98.50    0.50     0.5    0.50   11 × 10.sup.-1                    159   95.00    0.50     0.5    4.00   22 × 10.sup.-1                    160   95.49    4.00     0.5    0.01    9 × 10.sup.-1                    161   95.00    4.00     0.5    0.50   23 × 10.sup.-1                    162   91.50    4.00     0.5    4.00   44 × 10.sup.-1                    ______________________________________                                    

                  TABLE 21S                                                       ______________________________________                                        Test  Composition in percent  Resistivity,                                    No.   SrTiO.sub.3                                                                            Y.sub.2 O.sub.3                                                                        CuO    GeO.sub.2                                                                            ohm-cm                                  ______________________________________                                        163   99.48    0.01     0.5    0.01    8 × 10.sup.-1                    164   98.99    0.01     0.5    0.50   20 × 10.sup.-1                    165   95.49    0.01     0.5    4.00   37 × 10.sup.-1                    166   98.99    0.50     0.5    0.01    5 × 10.sup.-1                    167   98.50    0.50     0.5    0.50   12 × 10.sup.-1                    168   95.00    0.50     0.5    4.00   24 × 10.sup.-1                    169   95.49    4.00     0.5    0.01   11 × 10.sup.-1                    170   95.00    4.00     0.5    0.50   23 × 10.sup.-1                    171   91.50    4.00     0.5    4.00   41 × 10.sup.-1                    ______________________________________                                    

EXAMPLE 22

Fifteen different combinations of ingredients in accordance with theinvention were prepared as in TABLES 22A through 22-O, in order to makesure that two or more different metal oxides could be employed as thesecond, third, or fourth set of ingredients, in combination with SrTiO₃as the first ingredient. The various combinations of ingredients, eachin several different sets of proportions, were processed into ceramicdiscs through the same procedure as in EXAMPLE 1 except that thetemperature of the oxidative heat treatment was 1000° C. Theresistivities of these ceramic bodies, measured by the same method as inEXAMPLE 21, were as given in TABLES 22A through 22-O. The tabulatedresults demonstrate that the ceramic bodies made with the use of two ormore different metal oxides as the second, third, or fourth set ofingredients are all sufficiently semiconductive.

                                      TABLE 22A                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  Ta.sub.2 O.sub.5                                                                  CuO   GeO.sub.2                                                                         PbO                                                                              ZnO ohm-cm                                      __________________________________________________________________________    1  98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   5 × 10.sup.-1                         2  98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   7 × 10.sup.-1                         3  98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   6 × 10.sup.-1                         4  98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   7 × 10.sup.-1                         5  98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   3 × 10.sup.-1                         6  98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   4 × 10.sup.-1                         7  98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 9 × 10.sup.-1                         8  98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 11 × 10.sup.-1                        9  98.90 0 08                                                                              0.02                                                                              0.5   0   0  0.5 7 × 10.sup.-1                         __________________________________________________________________________

                                      TABLE 22B                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                          CuO   GeO.sub.2                                                                         PbO                                                                              ZnO ohm-cm                                      __________________________________________________________________________    10 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   7 × 10.sup.-1                         11 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   9 × 10.sup.-1                         12 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   6 × 10.sup.-1                         13 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   4 × 10.sup.-1                         14 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   5 × 10.sup.-1                         15 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   4 × 10.sup.-1                         16 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 6 × 10.sup.-1                         17 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 7 × 10.sup.-1                         18 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 3 × 10.sup.-1                         __________________________________________________________________________

                                      TABLE 22C                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  La.sub.2 O.sub.3                                                                  CuO   GeO.sub.2                                                                         PbO                                                                              ZnO ohm-cm                                      __________________________________________________________________________    19 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0    8 × 10.sup.-1                        20 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   13 × 10.sup.-1                        21 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   15 × 10.sup.-1                        22 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   10 × 10.sup.-1                        23 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   16 × 10.sup.-1                        24 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   21 × 10.sup.-1                        25 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 14 × 10.sup.-1                        26 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 15 × 10.sup.-1                        27 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 20 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22D                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  CeO.sub.2                                                                         CuO   GeO.sub.2                                                                         PbO                                                                              ZnO ohm-cm                                      __________________________________________________________________________    28 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   14 × 10.sup.-1                        29 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   19 × 10.sup.-1                        30 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   11 × 10.sup.-1                        31 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   23 × 10.sup.-1                        32 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   21 × 10.sup.-1                        33 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   13 × 10.sup.-1                        34 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 16 × 10.sup.-1                        35 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 29 × 10.sup.-1                        36 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 21 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22E                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  Dy.sub.2 O.sub.3                                                                  CuO   GeO.sub.2                                                                         PbO                                                                              ZnO ohm-cm                                      __________________________________________________________________________    37 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   8 × 10.sup.-1                         38 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   11 × 10.sup.-1                        39 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   10 × 10.sup.-1                        40 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   7 × 10.sup.-1                         41 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   9 × 10.sup.-1                         42 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   6 × 10.sup.-1                         43 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 6 × 10.sup.-1                         44 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 13 × 10.sup.-1                        45 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 9 × 10.sup.- 1                        __________________________________________________________________________

                                      TABLE 22F                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         La.sub.2 O.sub.3                                                                  Ta.sub.2 O.sub.5                                                                  CuO   GeO.sub.2                                                                         ZnO                                                                              B.sub.2 O.sub.3                                                                   ohm-cm                                      __________________________________________________________________________    46 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   11 × 10.sup.-1                        47 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   13 × 10.sup.-1                        48 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   15 × 10.sup.-1                        49 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   13 × 10.sup.-1                        50 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   16 × 16.sup.-1                        51 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   17 × 10.sup.-1                        52 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 13 × 10.sup.-1                        53 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 14 × 10.sup.-1                        54 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 16 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22G                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         La.sub.2 O.sub.3                                                                  WO.sub.3                                                                          CuO   GeO.sub.2                                                                         ZnO                                                                              B.sub.2 O.sub.3                                                                   ohm-cm                                      __________________________________________________________________________    55 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   12 × 10.sup.-1                        56 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   16 × 10.sup.-1                        57 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   21 × 10.sup.-1                        58 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   23 × 10.sup.-1                        59 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   24 × 10.sup.-1                        60 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   23 × 10.sup.-1                        61 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 29 × 10.sup.-1                        62 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 31 × 10.sup.-1                        63 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 30 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22H                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         La.sub.2 O.sub.3                                                                  CeO.sub.2                                                                         CuO   GeO.sub.2                                                                         ZnO                                                                              B.sub.2 O.sub.3                                                                   ohm-cm                                      __________________________________________________________________________    64 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   26 × 10.sup.-1                        65 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   23 × 10.sup.-1                        66 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   25 × 10.sup.-1                        67 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   31 × 10.sup.-1                        68 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   30 × 10.sup.-1                        69 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   29 × 10.sup.-1                        70 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 29 × 10.sup.-1                        71 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 36 × 10.sup.-1                        72 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 35 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22I                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  CuO   GeO.sub.2                                                                         ZnO                                                                              B.sub.2 O.sub.3                                                                   ohm-cm                                      __________________________________________________________________________    73 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   21 × 10.sup.-1                        74 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   20 × 10.sup.-1                        75 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   18 × 10.sup.-1                        76 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   17 × 10.sup.-1                        77 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   19 × 10.sup.-1                        78 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   13 × 10.sup.-1                        79 98.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 22 × 10.sup.-1                        80 98.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 21 × 10.sup.-1                        81 98.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 19 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22J                                   __________________________________________________________________________    Composition in percent                                                           First Second  Third Fourth                                                 Test                                                                             ingredient                                                                          ingredients                                                                           ingredient                                                                          ingredients                                                                              Resistivity,                                No.                                                                              SrTiO.sub.3                                                                         La.sub.2 O.sub.3                                                                  Sm.sub.2 O.sub.3                                                                  CuO   GeO.sub.2                                                                         ZnO                                                                              B.sub.2 O.sub.3                                                                   ohm-cm                                      __________________________________________________________________________    82 98.90 0.02                                                                              0.08                                                                              0.5   0.5 0  0   29 × 10.sup.-1                        83 98.90 0.05                                                                              0.05                                                                              0.5   0.5 0  0   30 × 10.sup.-1                        84 98.90 0.08                                                                              0.02                                                                              0.5   0.5 0  0   33 × 10.sup.-1                        85 98.90 0.02                                                                              0.08                                                                              0.5   0   0.5                                                                              0   28 × 10.sup.-1                        86 98.90 0.05                                                                              0.05                                                                              0.5   0   0.5                                                                              0   32 × 10.sup.-1                        87 98.90 0.08                                                                              0.02                                                                              0.5   0   0.5                                                                              0   35 × 10.sup.-1                        88 89.90 0.02                                                                              0.08                                                                              0.5   0   0  0.5 34 × 10.sup.-1                        89 89.90 0.05                                                                              0.05                                                                              0.5   0   0  0.5 36 × 10.sup.-1                        90 89.90 0.08                                                                              0.02                                                                              0.5   0   0  0.5 39 × 10.sup.-1                        __________________________________________________________________________

                                      TABLE 22K                                   __________________________________________________________________________    Composition in percent                                                           First Second     Third  Fourth                                             Test                                                                             ingredient                                                                          ingredients                                                                              ingredients                                                                          ingredient                                                                          Resistivity,                                 No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                         La.sub.2 O.sub.3                                                                  CuO                                                                              Cu.sub.2 O                                                                        GeO.sub.2                                                                           ohm-cm                                       __________________________________________________________________________    91 98.90 0.1 0  0   0.1                                                                              0.4 0.5   9 × 10.sup.-1                          92 98.90 0.1 0  0   0.25                                                                             0.25                                                                              0.5   12 × 10.sup.-1                         93 98.90 0.1 0  0   0.4                                                                              0.1 0.5   6 × 10.sup.-1                          94 98.90 0   0.1                                                                              0   0.1                                                                              0.4 0.5   11 × 10.sup.-1                         95 98.90 0   0.1                                                                              0   0.25                                                                             0.25                                                                              0.5   13 × 10.sup.-1                         96 98.90 0   0.1                                                                              0   0.4                                                                              0.1 0.5   8 × 10.sup.-1                          97 98.90 0   0  0.1 0.1                                                                              0.4 0.5   9 × 10.sup.-1                          98 98.90 0   0  0.1 0.25                                                                             0.25                                                                              0.5   9 × 10.sup.-1                          99 98.90 0   0  0.1 0.4                                                                              0.1 0.5   7 × 10.sup. -1                         __________________________________________________________________________

                                      TABLE 22L                                   __________________________________________________________________________    Composition in percent                                                           First Second     Third  Fourth                                             Test                                                                             ingredient                                                                          ingredients                                                                              ingredients                                                                          ingredient                                                                          Resistivity,                                 No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                         La.sub.2 O.sub.3                                                                  CuO                                                                              MoO.sub.3                                                                         GeO.sub.2                                                                           ohm-cm                                       __________________________________________________________________________    100                                                                              98.90 0.1 0  0   0.1                                                                              0.4 0.5   6 × 10.sup.-1                          101                                                                              98.90 0.1 0  0   0.25                                                                             0.25                                                                              0.5   7 × 10.sup.-1                          102                                                                              98.90 0.1 0  0   0.4                                                                              0.1 0.5   5 × 10.sup.-1                          103                                                                              98.90 0   0.1                                                                              0   0.1                                                                              0.4 0.5   7 × 10.sup.-1                          104                                                                              98.90 0   0.1                                                                              0   0.25                                                                             0.25                                                                              0.5   6 × 10.sup.-1                          105                                                                              98.90 0   0.1                                                                              0   0.4                                                                              0.1 0.5   7 × 10.sup.-1                          106                                                                              98.90 0   0  0.1 0.1                                                                              0.4 0.5   6 × 10.sup.-1                          107                                                                              98.90 0   0  0.1 0.25                                                                             0.25                                                                              0.5   8 × 10.sup.-1                          108                                                                              98.90 0   0  0.1 0.4                                                                              0.1 0.5   11 × 10.sup.-1                         __________________________________________________________________________

                                      TABLE 22M                                   __________________________________________________________________________    Composition in percent                                                           First Second     Third  Fourth                                             Test                                                                             ingredient                                                                          ingredients                                                                              ingredients                                                                          ingredient                                                                          Resistivity,                                 No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                         La.sub.2 O.sub.3                                                                  MoO.sub.3                                                                        V.sub.2 O.sub.5                                                                   GeO.sub.2                                                                           ohm-cm                                       __________________________________________________________________________    109                                                                              98.90 0.1 0  0   0.1                                                                              0.4 0.5   11 × 10.sup.-1                         110                                                                              98.90 0.1 0  0   0.25                                                                             0.25                                                                              0.5   13 × 10.sup.-1                         111                                                                              98.90 0.1 0  0   0.4                                                                              0.1 0.5   14 × 10.sup.-1                         112                                                                              98.90 0   0.1                                                                              0   0.1                                                                              0.4 0.5   15 × 10.sup.-1                         113                                                                              98.90 0   0.1                                                                              0   0.25                                                                             0.25                                                                              0.5   10 × 10.sup.-1                         114                                                                              98.90 0   0.1                                                                              0   0.4                                                                              0.1 0.5   11 × 10.sup.-1                         115                                                                              98.90 0   0  0.1 0.1                                                                              0.4 0.5   17 × 10.sup.-1                         116                                                                              98.90 0   0  0.1 0.25                                                                             0.25                                                                              0.5   14 × 10.sup.-1                         117                                                                              98.90 0   0  0.1 0.4                                                                              0.1 0.5   15 × 10.sup.-1                         __________________________________________________________________________

                                      TABLE 22N                                   __________________________________________________________________________    Composition in percent                                                           First Second     Third  Fourth                                             Test                                                                             ingredient                                                                          ingredients                                                                              ingredients                                                                          ingredient                                                                          Resistivity,                                 No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                         La.sub.2 O.sub.3                                                                  V.sub.2 O.sub.5                                                                  CrO.sub.3                                                                         GeO.sub.2                                                                           ohm-cm                                       __________________________________________________________________________    118                                                                              98.90 0.1 0  0   0.1                                                                              0.4 0.5   7 × 10.sup.-1                          119                                                                              98.90 0.1 0  0   0.25                                                                             0.25                                                                              0.5   9 × 10.sup.-1                          120                                                                              98.90 0.1 0  0   0.4                                                                              0.1 0.5   8 × 10.sup.-1                          121                                                                              98.90 0   0.1                                                                              0   0.1                                                                              0.4 0.5   3 × 10.sup.-1                          122                                                                              98.90 0   0.1                                                                              0   0.25                                                                             0.25                                                                              0.5   6 × 10.sup.-1                          123                                                                              98.90 0   0.1                                                                              0   0.4                                                                              0.1 0.5   9 × 10.sup.-1                          124                                                                              98.90 0   0  0.1 0.1                                                                              0.4 0.5   8 × 10.sup.-1                          125                                                                              98.90 0   0  0.1 0.25                                                                             0.25                                                                              0.5   9 × 10.sup.-1                          126                                                                              98.90 0   0  0.1 0.4                                                                              0.1 0.5   9 × 10.sup.-1                          __________________________________________________________________________

                                      TABLE 22-O                                  __________________________________________________________________________    Composition in percent                                                           First Second     Third  Fourth                                             Test                                                                             ingredient                                                                          ingredients                                                                              ingredients                                                                          ingredient                                                                          Resistivity,                                 No.                                                                              SrTiO.sub.3                                                                         Nb.sub.2 O.sub.5                                                                  WO.sub.3                                                                         La.sub.2 O.sub.3                                                                  CrO.sub.3                                                                        Cu.sub.2 O                                                                        GeO.sub.2                                                                           ohm-cm                                       __________________________________________________________________________    127                                                                              98.90 0.1 0  0   0.1                                                                              0.4 0.5   10 × 10.sup.-1                         128                                                                              98.90 0.1 0  0   0.25                                                                             0.25                                                                              0.5    9 × 10.sup.-1                         129                                                                              98.90 0.1 0  0   0.4                                                                              0.1 0.5    7 × 10.sup.-1                         130                                                                              98.90 0   0.1                                                                              0   0.1                                                                              0.4 0.5   11 × 10.sup.-1                         131                                                                              98.90 0   0.1                                                                              0   0.25                                                                             0.25                                                                              0.5   12 × 10.sup.-1                         132                                                                              98.90 0   0.1                                                                              0   0.4                                                                              0.1 0.5   11 × 10.sup.-1                         133                                                                              98.90 0   0  0.1 0.1                                                                              0.4 0.5   13 × 10.sup.-1                         134                                                                              98.90 0   0  0.1 0.25                                                                             0.25                                                                              0.5   11 × 10.sup.-1                         135                                                                              98.90 0   0  0.1 0.4                                                                              0.1 0.5    9 × 10.sup.- 1                        __________________________________________________________________________

EXAMPLE 23

Six different combinations of four ingredients chosen in accordance withthe invention, each in a fixed set of proportions, were prepared as inTABLES 23A through 23F, in order to to study the relationship betweenthe temperatures of the oxidative heat treatment and the characteristicsof the resulting ceramic bodies and varistors. The tabulatedcombinations of ingredients were processed into ceramic discs, andfurther into varistors, through the same procedure as in EXAMPLE 1except that the temperature of the oxidative heat treatment was set atvarious values from 700° to 1170° C. TABLES 23A through 23F alsorepresent the E₁₀, α, and resistivity of the thus-fabricated ceramicbodies and varistors. The E₁₀ of the varistors oxidatively heat-treatedat 700° and 800° C. was not measured.

                                      TABLE 23A                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  CuO GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________    1  98.9                                                                              0.1 0.5 0.5 700     --  1  6 × 10.sup.-1                         2  98.9                                                                              0.1 0.5 0.5 800     --  1  2                                           3  98.9                                                                              0.1 0.5 0.5 900      4  4  4 × 10.sup.2                          4  98.9                                                                              0.1 0.5 0.5 1000    14  6  1 × 10.sup.3                          5  98.9                                                                              0.1 0.5 0.5 1100    36  17 4 × 10.sup.3                          6  98.9                                                                              0.1 0.5 0.5 1170    68  26 7 × 10.sup.3                          __________________________________________________________________________

                                      TABLE 23B                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  Cu.sub.2 O                                                                        GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________     7 98.9                                                                              0.1 0.5 0.5  700    --  1  7 × 10.sup.-1                          8 98.9                                                                              0.1 0.5 0.5  800    --  1  5                                            9 98.9                                                                              0.1 0.5 0.5  900     4  4  3 × 10.sup.2                          10 98.9                                                                              0.1 0.5 0.5 1000    17  8  2 × 10.sup.3                          11 98.9                                                                              0.1 0.5 0.5 1100    44  21 4 × 10.sup.3                          12 98.9                                                                              0.1 0.5 0.5 1170    99  35 1 × 10.sup.4                          __________________________________________________________________________

                                      TABLE 23C                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  V.sub.2 O.sub.5                                                                   GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________    13 98.9                                                                              0.1 0.5 0.5  700    --  1  9 × 10.sup.-1                         14 98.9                                                                              0.1 0.5 0.5  800    --  1  6                                           15 98.9                                                                              0.1 0.5 0.5  900     5  4  4 × 10.sup.2                          16 98.9                                                                              0.1 0.5 0.5 1000    14  6  2 × 10.sup.3                          17 98.9                                                                              0.1 0.5 0.5 1100    35  16 3 × 10.sup.3                          18 98.9                                                                              0.1 0.5 0.5 1170    67  29 7 × 10.sup.3                          __________________________________________________________________________

                                      TABLE 23D                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  CrO.sub.3                                                                         GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________    19 98.9                                                                              0.1 0.5 0.5  700    --  1  8 × 10.sup.-1                         20 98.9                                                                              0.1 0.5 0.5  800    --  1  5                                           21 98.9                                                                              0.1 0.5 0.5  900     6  4  5 × 10.sup.2                          22 98.9                                                                              0.1 0.5 0.5 1000    15  7  2 × 10.sup.3                          23 98.9                                                                              0.1 0.5 0.5 1100    40  20 4 × 10.sup.3                          24 98.9                                                                              0.1 0.5 0.5 1170    82  33 8 × 10.sup.3                          __________________________________________________________________________

                                      TABLE 23E                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  MoO.sub.3                                                                         GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________    25 98.9                                                                              0.1 0.5 0.5  700    --  1  6 × 10.sup.-1                         26 98.9                                                                              0.1 0.5 0.5  800    --  1  3                                           27 98.9                                                                              0.1 0.5 0.5  900     3  4  5 × 10.sup.2                          28 98.9                                                                              0.1 0.5 0.5 1000    13  6  1 × 10.sup.3                          29 98.9                                                                              0.1 0.5 0.5 1100    41  21 4 × 10.sup.3                          30 98.9                                                                              0.1 0.5 0.5 1170    82  31 9 × 10.sup.3                          __________________________________________________________________________

                                      TABLE 23F                                   __________________________________________________________________________                       Temperature of                                                                        Properties                                         Test                                                                             Composition in percent                                                                        oxidative heat Resistivity,                                No.                                                                              SrTiO.sub.3                                                                       Nb.sub.2 O.sub.5                                                                  MnO.sub.2                                                                         GeO.sub.2                                                                         treatment, °C.                                                                 E.sub.10, V                                                                       α                                                                          ohm-cm                                      __________________________________________________________________________    31 98.9                                                                              0.1 0.5 0.5  700    --  1  .sup. 8 × 10.sup.-1                   32 98.9                                                                              0.1 0.5 0.5  800    --  2  3                                           33 98.9                                                                              0.1 0.5 0.5  900     4  4  4 × 10.sup.2                          34 98.9                                                                              0.1 0.5 0.5 1000    14  6  2 × 10.sup.3                          35 98.9                                                                              0.1 0.5 0.5 1100    39  18 4 × 10.sup.3                          36 98.9                                                                              0.1 0.5 0.5 1170    89  31 8 × 10.sup.4                          __________________________________________________________________________

Based on the data given in TABLE 23A, FIG. 7 graphically represents thecurve of the α of the SrTiO₃ --Nb₂ O₅ --CuO--GeO₂ varistors against thetemperature of the oxidative heat treatment. The graph exhibits someproportionality between the two factors, making clear that the α of thevaristors can be controlled by the temperature of the oxidative heattreatment during the fabrication of the ceramic bodies. A comparison ofthis graph with that of FIG. 6, which plots a similar curve in the casewhere the ceramic composition contains no fourth ingredient, will revealthat the α of the varistors including the fourth ingredient varies lesswith the temperature and so is easier to control.

The curve C in the graph of FIG. 8 represents the E₁₀ of the SrTiO₃--Nb₂ O₅ --CuO--GeO₂ varistors plotted against the temperature of theoxidative heat treatment, on the basis of the data also given in TABLE23A. The curve indicates that the E₁₀ of the varistors can likewise becontrolled by the temperature of the oxidative heat treatment.

By way of comparison several ceramic bodies were prepared from 99.4%SrTiO₃, 0.1% Nb₂ O₅, and 0.5% CuO, with no fourth ingredient added, byprogressively varying the temperature of the oxidative heat treatment.The curve D in FIG. 8 represents the E₁₀ of the varistors made fromthese ceramic bodies, plotted agaist the temperature of the oxidativeheat treatment. As will be understood upon comparison of the curves Cand D, the addition of the fourth ingredient makes less the change ofE₁₀ with temperature. When 10 SrTiO₃ --Nb₂ O₅ --CuO varistors wereproduced, with the temperature of the oxidative heat treatment set at1000° C., their E₁₀ varied between 33 and 53 V, averaging 44 V. Therewas thus a difference of as much as 20 V between the maximum and minimumvalues. Constrastively, when another ten varistors were prepared byadding GeO₂ as the fourth ingredient to the above composition, with thetemperature of the oxidative heat treatment also set at 1000° C., theirE₁₀ varied only between 12 and 16 V, averaging 14 V. Thus the additionof the fourth ingredient greatly reduces fluctuations in E₁₀. Suchreduction of fluctuations in E₁₀ and α results, obviously, from thehigher coherency of the ceramic bodies and greater uniformity ofparticle size, brought about by the introduction of the fourthingredient.

When the temperature of the oxidative heat treatment was below 900° C.,the resistivity of the ceramic bodies became too low, and when thetemperature was above 1300° C., the resistivity became too high forvaristors. The oxidative heat treatment should therefore be conducted ina temperature range of about 900°-1300° C., preferably about 900°-1170°C.

EXAMPLE 24

Varistors incorporating a fourth ingredient were tested as to theirpulse-withstanding abilities in this EXAMPLE. Ceramic discs wereprepared from six different combinations of four possible ingredientsgiven in TABLE 24, in like proportions, and were processed intovaristors, through the same procedure as in EXAMPLE 1 except that thetemperature of the oxidative heat treatment was 1000° C. As in EXAMPLE14, 10 voltage pulses of 100 V were successively applied to eachvaristor, and a rate of change in E₁₀ before and after the pulseapplication was computed. TABLE 24 shows the results.

                  TABLE 24                                                        ______________________________________                                        Composition                                                                        First     Second    Third   Fourth  Change                               Test ingredient                                                                              ingredient                                                                              ingredient                                                                            ingredient                                                                            in                                   No.  (98.9%)   (0.1%)    (0.5%)  (0.5%)  E.sub.10, %                          ______________________________________                                        1    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.5                                                                        V.sub.2 O.sub.5                                                                       GeO.sub.2                                                                             -0.05                                2    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.5                                                                        CrO.sub.3                                                                             GeO.sub.2                                                                             -0.03                                3    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.2                                                                        CuO     GeO.sub.2                                                                             -0.01                                4    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.5                                                                        Cu.sub.2 O                                                                            GeO.sub.2                                                                             -0.03                                5    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.5                                                                        MoO.sub.3                                                                             GeO.sub.2                                                                             -0.06                                6    SrTiO.sub.3                                                                             Nb.sub.2 O.sub.5                                                                        MnO.sub.2                                                                             GeO.sub.2                                                                             -0.05                                ______________________________________                                    

EXAMPLE 25

Six different combinations of four possible ingredients in accordancewith the invention, each in different sets of proportions, were preparedas in TABLES 25A through 25F. The various combinations of ingredientswere processed into ceramic discs, and further into varistors, throughthe same procedure as in EXAMPLE 1 except that the temperature of theoxidative heat treatment was 1000° C. In order to In order to examinevariations in the E₁₀ of the varistors with temperatures at which theyare put to use, the temperature change Tc₂₅₋₅₀ of the E₁₀ of eachvaristor was computed from the equation, Tc₂₅₋₅₀ =(A-B)100/A, where A isthe value of E₁₀ at 25° C., and B is the value of E₁₀ at 50° C. TABLES25A through 25F show the results.

                  TABLE 25A                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       CuO    GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        1    99.48    0.01     0.01   0.5    -0.07                                    2    98.99    0.01     0.50   0.5    -0.07                                    3    94.49    0.01     5.00   0.5    -0.06                                    4    99.39    0.10     0.01   0.5    -0.06                                    5    98.90    0.10     0.50   0.5    -0.05                                    6    94.40    0.10     5.00   0.5    -0.05                                    7    96.99    2.5      0.01   0.5    -0.06                                    8    96.50    2.5      0.50   0.5    -0.05                                    9    92.00    2.5      5.00   0.5    -0.05                                    ______________________________________                                    

                  TABLE 25B                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       Cu.sub.2 O                                                                           GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        10   99.48    0.01     0.01   0.5    -0.07                                    11   98.99    0.01     0.50   0.5    -0.06                                    12   96.99    0.01     2.50   0.5    -0.05                                    13   99.39    0.10     0.01   0.5    -0.06                                    14   98.90    0.10     0.50   0.5    -0.06                                    15   96.90    0.10     2.50   0.5    -0.05                                    16   96.99    2.5      0.01   0.5    -0.06                                    17   96.50    2.5      0.50   0.5    -0.05                                    18   94.50    2.5      2.50   0.5    -0.05                                    ______________________________________                                    

                  TABLE 25C                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       V.sub.2 O.sub.5                                                                      GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        19   99.48    0.01     0.01   0.5    -0.06                                    20   98.99    0.01     0.50   0.5    -0.06                                    21   98.49    0.01     1.00   0.5    -0.05                                    22   99.39    0.10     0.01   0.5    -0.05                                    23   98.90    0.10     0.50   0.5    -0.06                                    24   98.40    0.10     1.00   0.5    -0.07                                    25   96.99    2.5      0.01   0.5    -0.06                                    26   96.50    2.5      0.50   0.5    -0.06                                    27   96.00    2.5      1.00   0.5    -0.05                                    ______________________________________                                    

                  TABLE 25D                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       CrO.sub.3                                                                            GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        28   99.48    0.01     0.01   0.5    -0.07                                    29   98.99    0.01     0.50   0.5    -0.06                                    30   97.49    0.01     2.00   0.5    -0.06                                    31   99.39    0.10     0.01   0.5    -0.07                                    32   98.90    0.10     0.50   0.5    -0.07                                    33   97.40    0.10     2.00   0.5    -0.05                                    34   96.99    2.5      0.01   0.5    -0.06                                    35   96.50    2.5      0.50   0.5    -0.07                                    36   95.00    2.5      2.00   0.5    -0.05                                    ______________________________________                                    

                  TABLE 25E                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       MoO.sub.3                                                                            GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        37   99.48    0.01     0.01   0.5    -0.07                                    38   98.99    0.01     0.50   0.5    -0.06                                    39   94.49    0.01     5.00   0.5    -0.06                                    40   99.39    0.10     0.01   0.5    -0.07                                    41   98.90    0.10     0.50   0.5    -0.07                                    42   94.40    0.10     5.00   0.5    -0.06                                    43   96.99    2.50     0.01   0.5    -0.06                                    44   96.50    2.50     0.50   0.5    -0.05                                    45   92.00    2.50     5.00   0.5    -0.05                                    ______________________________________                                    

                  TABLE 25F                                                       ______________________________________                                                                     Temperature                                      Test Composition in percent  change Tc.sub.25-50                              No.  SrTiO.sub.3                                                                            Nb.sub.2 O.sub.5                                                                       MnO.sub.2                                                                            GeO.sub.2                                                                            of E.sub.10, %                           ______________________________________                                        46   99.48    0.01     0.01   0.5    -0.07                                    47   98.99    0.01     0.50   0.5    -0.06                                    48   96.99    0.01     2.50   0.5    -0.06                                    49   99.39    0.10     0.01   0.5    -0.06                                    50   98.90    0.10     0.50   0.5    -0.06                                    51   96.90    0.10     2.50   0.5    -0.05                                    52   96.99    2.50     0.01   0.5    -0.05                                    53   96.50    2.50     0.50   0.5    -0.05                                    54   94.50    2.50     2.50   0.5    -0.05                                    ______________________________________                                    

The tabulated results all indicate little changes in the E₁₀ of thevaristors with the temperatures at which they operate. It can beconcluded from this that the operating temperatures of the varistorsprepared in accordance with the invention hardly affect theirperformance.

By way of example the E₁₀ of the varistor of Test No. 5 in TABLE 25A wasfurther measured at temperatures of -20°, 0°, +80° and +100° C. Thecurve E in the graph of FIG. 9 represents the relation, (A-C)100/A, ofthis varistor, where A is as defined above and C is the value of E₁₀ ateach of the other temperatures. The curve F in the same graph plots asimilar relation of the varistor of Test No. 41 in TABLE 25E. The curvesshow little changes in the E₁₀ of the exemplified varistors over a widetemperature range. Obviously, the same holds true with the othervaristors manufactured in accordance with the invention.

It is to be understood that the foregoing EXAMPLES are meant purely toillustrate or explain and not to impose limitations upon the invention.Experiment has proved, for example, that alumina, silica and otheradditives might be used insofar as they do not impair the desiredproperties of the ceramic materials in accordance with the invention. Ithas also been confirmed that the addition of up to 1.5% bismuthtrioxide, with a view to the control of particle size, firingtemperature, etc., does not adversely affect the desired properties ofthe ceramic materials. The appended claims should therefore be construedto specify only the fundamental ingredients of the inventive ceramics.

What is claimed is:
 1. A process for the fabrication of coherent bondedbodies of a semiconductive ceramic composition with a nonlinearvolt-ampere characteristic, particularly well suited for use invaristors, which comprises:(a) providing a mixture of: SrTiO₃ in finelydivided form;(2) from about 0.001 to about 5.000% of at least one metaloxide in finely divided form, for making the composition semiconductive,selected from the group consisting of Nb₂ O₅, Ta₂ O₅, WO₃, La₂ O₃, CeO₂,Nd₂ O₃, Pr₆ O₁₁, Dy₂ O₃, Y₂ O₃, and Sm₂ O₃ ; (3) from about 0.010 toabout 5.000% of at least one other metal oxide in finely divided form,for improving the nonlinear volt-ampere characteristic of thecomposition, selected from the group consisting of V₂ O₅, Cr₂ O₃, CuO,Cu₂ O, MoO₃, and MnO₂ ; and (4) a binder; (b) molding the mixture intobodies of desired shape under pressure; (c) firing the bodies in atemperature range of from about 1300° to about 1500° C. in anonoxidative atmosphere; and (d) heating the fired bodies in atemperature range of from about 800° to about 1300° C. in an oxidativeatmosphere.
 2. A process for the fabrication of coherent bonded bodiesof a semiconductive ceramic composition with a nonlinear volt-amperecharacteristic, particularly well suited for use in varistors, whichcomprises:(a) providing a mixture of:(1) from about 86.000 to about99.979% SrTiO₃ in finely divided form; (2) from about 0.001 to about5.000% of at least one metal oxide in finely divided form, for makingthe composition semiconductive, selected from the group consisting ofNb₂ O₅, Ta₂ O₅, WO₃, La₂ O₃, CeO₂, Nd₂ O₃, Pr₆ O₁₁, Dy₂ O₃, Y₂ O₃, andSm₂ O₃ ; (3) from about 0.010 to about 5.000% of at least one othermetal oxide in finely divided form, for improving the nonlinearvolt-ampere characteristic of the composition, selected from the groupconsisting of V₂ O₅, Cr₂ O₃, CuO, Cu₂ O, MoO₃, and MnO₂ ; (4) from about0.010 to about 4.000% of at least one still other metal oxide in finelydivided form, for improving the coherency of the bodies of thecomposition, selected from the group consisting of GeO₂, ZnO, B₂ O₃, andPbO; and (5) a binder; (b) molding the mixture into bodies of desiredshape under pressure; (c) firing the bodies in a temperature range offrom about 1300° to about 1500° C. in a nonoxidative atmosphere; and (d)heating the fired bodies in a temperature range of from about 900° toabout 1300° C. in an oxidative atmosphere.
 3. A process according toclaims 1 or 2, wherein the mixture is molded at pressures ranging fromabout 500 to about 2000 kg/cm².
 4. A process according to claims 1 or 2,wherein the molded bodies are fired in a reductive atmosphere.
 5. Aprocess according to claim 4, wherein the atmosphere is about 95 volume% molecular nitrogen and about five volume % molecular hydrogen.
 6. Aprocess according to claims 1 or 2, wherein the binder is polyvinylalcohol.